Decouple poller from plugin manager.

Generate and store handshake key pair at startup if necessary

Closes #1538

See merge request briar/briar!1082

.idea/codeStyles/Project.xml

@@ -39,31 +39,6 @@
     <JetCodeStyleSettings>
       <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
     </JetCodeStyleSettings>
-    <Objective-C-extensions>
-      <file>
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Import" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Macro" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Typedef" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Enum" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Constant" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Global" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Struct" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="FunctionPredecl" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Function" />
-      </file>
-      <class>
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Property" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="Synthesize" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="InitMethod" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="StaticMethod" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="InstanceMethod" />
-        <option name="com.jetbrains.cidr.lang.util.OCDeclarationKind" value="DeallocMethod" />
-      </class>
-      <extensions>
-        <pair source="cpp" header="h" fileNamingConvention="NONE" />
-        <pair source="c" header="h" fileNamingConvention="NONE" />
-      </extensions>
-    </Objective-C-extensions>
     <XML>
       <option name="XML_LEGACY_SETTINGS_IMPORTED" value="true" />
     </XML>

bramble-android/build.gradle

@@ -11,8 +11,8 @@ android {
 	defaultConfig {
 		minSdkVersion 14
 		targetSdkVersion 26
-		versionCode 10105
-		versionName "1.1.5"
+		versionCode 10106
+		versionName "1.1.6"
 		consumerProguardFiles 'proguard-rules.txt'
 
 		testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
@@ -30,10 +30,10 @@ configurations {
 
 dependencies {
 	implementation project(path: ':bramble-core', configuration: 'default')
-	tor 'org.briarproject:tor-android:0.3.4.8@zip'
-	tor 'org.briarproject:obfs4proxy-android:0.0.7@zip'
+	tor 'org.briarproject:tor-android:0.3.5.8@zip'
+	tor 'org.briarproject:obfs4proxy-android:0.0.9@zip'
 
-	annotationProcessor 'com.google.dagger:dagger-compiler:2.19'
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.22.1'
 
 	compileOnly 'javax.annotation:jsr250-api:1.0'
 

bramble-android/src/main/java/org/briarproject/bramble/account/AndroidAccountManager.java

@@ -12,11 +12,15 @@ import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.util.IoUtils;
 
 import java.io.File;
+import java.util.HashSet;
+import java.util.Set;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import static android.os.Build.VERSION.SDK_INT;
+
 class AndroidAccountManager extends AccountManagerImpl
 		implements AccountManager {
 
@@ -89,20 +93,42 @@ class AndroidAccountManager extends AccountManagerImpl
 				LOG.warning("Could not clear shared preferences");
 		}
 		// Delete files, except lib and shared_prefs directories
+		Set<File> files = new HashSet<>();
 		File dataDir = new File(appContext.getApplicationInfo().dataDir);
-		File[] children = dataDir.listFiles();
-		if (children == null) {
+		@Nullable
+		File[] fileArray = dataDir.listFiles();
+		if (fileArray == null) {
 			LOG.warning("Could not list files in app data dir");
 		} else {
-			for (File child : children) {
-				String name = child.getName();
+			for (File file : fileArray) {
+				String name = file.getName();
 				if (!name.equals("lib") && !name.equals("shared_prefs")) {
-					IoUtils.deleteFileOrDir(child);
+					files.add(file);
 				}
 			}
 		}
+		files.add(appContext.getFilesDir());
+		files.add(appContext.getCacheDir());
+		addIfNotNull(files, appContext.getExternalCacheDir());
+		if (SDK_INT >= 19) {
+			for (File file : appContext.getExternalCacheDirs()) {
+				addIfNotNull(files, file);
+			}
+		}
+		if (SDK_INT >= 21) {
+			for (File file : appContext.getExternalMediaDirs()) {
+				addIfNotNull(files, file);
+			}
+		}
+		for (File file : files) {
+			IoUtils.deleteFileOrDir(file);
+		}
 		// Recreate the cache dir as some OpenGL drivers expect it to exist
-		if (!new File(dataDir, "cache").mkdir())
+		if (!new File(dataDir, "cache").mkdirs())
 			LOG.warning("Could not recreate cache dir");
 	}
+
+	private void addIfNotNull(Set<File> files, @Nullable File file) {
+		if (file != null) files.add(file);
+	}
 }

bramble-android/src/main/java/org/briarproject/bramble/battery/AndroidBatteryManager.java

@@ -19,9 +19,7 @@ import javax.inject.Inject;
 import static android.content.Intent.ACTION_BATTERY_CHANGED;
 import static android.content.Intent.ACTION_POWER_CONNECTED;
 import static android.content.Intent.ACTION_POWER_DISCONNECTED;
-import static android.os.BatteryManager.BATTERY_STATUS_CHARGING;
-import static android.os.BatteryManager.BATTERY_STATUS_FULL;
-import static android.os.BatteryManager.EXTRA_STATUS;
+import static android.os.BatteryManager.EXTRA_PLUGGED;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Logger.getLogger;
 
@@ -48,9 +46,8 @@ class AndroidBatteryManager implements BatteryManager, Service {
 		IntentFilter filter = new IntentFilter(ACTION_BATTERY_CHANGED);
 		Intent i = appContext.registerReceiver(null, filter);
 		if (i == null) return false;
-		int status = i.getIntExtra(EXTRA_STATUS, -1);
-		return status == BATTERY_STATUS_CHARGING ||
-				status == BATTERY_STATUS_FULL;
+		int status = i.getIntExtra(EXTRA_PLUGGED, 0);
+		return status != 0;
 	}
 
 	@Override

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPlugin.java

@@ -32,9 +32,6 @@ import static java.util.concurrent.TimeUnit.MINUTES;
 @ParametersNotNullByDefault
 class AndroidTorPlugin extends TorPlugin {
 
-	// This tag may prevent Huawei's power manager from killing us
-	private static final String WAKE_LOCK_TAG = "LocationManagerService";
-
 	private final Context appContext;
 	private final RenewableWakeLock wakeLock;
 
@@ -55,7 +52,7 @@ class AndroidTorPlugin extends TorPlugin {
 				appContext.getSystemService(POWER_SERVICE);
 		if (pm == null) throw new AssertionError();
 		wakeLock = new RenewableWakeLock(pm, scheduler, PARTIAL_WAKE_LOCK,
-				WAKE_LOCK_TAG, 1, MINUTES);
+				getWakeLockTag(), 1, MINUTES);
 	}
 
 	@Override
@@ -87,4 +84,17 @@ class AndroidTorPlugin extends TorPlugin {
 		super.stop();
 		wakeLock.release();
 	}
+
+	private String getWakeLockTag() {
+		PackageManager pm = appContext.getPackageManager();
+		for (PackageInfo info : pm.getInstalledPackages(0)) {
+			String name = info.packageName.toLowerCase();
+			if (name.startsWith("com.huawei.powergenie")) {
+				return "LocationManagerService";
+			} else if (name.startsWith("com.evenwell.powermonitor")) {
+				return "AudioIn";
+			}
+		}
+		return getClass().getSimpleName();
+	}
 }

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidSystemModule.java

@@ -1,10 +1,13 @@
 package org.briarproject.bramble.system;
 
+import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
 import org.briarproject.bramble.api.system.SecureRandomProvider;
 
+import java.util.concurrent.Executor;
+
 import javax.inject.Singleton;
 
 import dagger.Module;
@@ -32,6 +35,13 @@ public class AndroidSystemModule {
 		return androidExecutor;
 	}
 
+	@Provides
+	@Singleton
+	@EventExecutor
+	Executor provideEventExecutor(AndroidExecutor androidExecutor) {
+		return androidExecutor::runOnUiThread;
+	}
+
 	@Provides
 	@Singleton
 	ResourceProvider provideResourceProvider(AndroidResourceProvider provider) {

bramble-android/src/test/java/org/briarproject/bramble/account/AndroidAccountManagerTest.java

@@ -112,6 +112,8 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 		// Other directories should be deleted
 		File potatoDir = new File(testDir, ".potato");
 		File potatoFile = new File(potatoDir, "file");
+		File filesDir = new File(testDir, "filesDir");
+		File externalCacheDir = new File(testDir, "externalCacheDir");
 
 		context.checking(new Expectations() {{
 			oneOf(prefs).edit();
@@ -128,6 +130,12 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 			will(returnValue(true));
 			oneOf(app).getApplicationInfo();
 			will(returnValue(applicationInfo));
+			oneOf(app).getFilesDir();
+			will(returnValue(filesDir));
+			oneOf(app).getCacheDir();
+			will(returnValue(cacheDir));
+			oneOf(app).getExternalCacheDir();
+			will(returnValue(externalCacheDir));
 		}});
 
 		assertTrue(dbDir.mkdirs());
@@ -140,6 +148,8 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 		assertTrue(cacheFile.createNewFile());
 		assertTrue(potatoDir.mkdirs());
 		assertTrue(potatoFile.createNewFile());
+		assertTrue(filesDir.mkdirs());
+		assertTrue(externalCacheDir.mkdirs());
 
 		accountManager.deleteAccount();
 
@@ -153,6 +163,8 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 		assertFalse(cacheFile.exists());
 		assertFalse(potatoDir.exists());
 		assertFalse(potatoFile.exists());
+		assertFalse(filesDir.exists());
+		assertFalse(externalCacheDir.exists());
 	}
 
 	@After

bramble-android/witness.gradle

@@ -1,47 +1,45 @@
 dependencyVerification {
     verify = [
         'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
-        'com.android.tools.analytics-library:protos:26.2.1:protos-26.2.1.jar:2f371f5b1f551e85ab08be4d6a2873471b3d44afd1ebf6aa3298f3b796bf691f',
-        'com.android.tools.analytics-library:shared:26.2.1:shared-26.2.1.jar:4c1e4e705fa4d45f23aaea230557f6508155012d9c296337787c1d7b26a97f5a',
-        'com.android.tools.analytics-library:tracker:26.2.1:tracker-26.2.1.jar:4a624ecc976539f755ddb0bb8dfc2dd3d08326cfec59a098dbd70f701ca7fb75',
-        'com.android.tools.build:aapt2:3.2.1-4818971:aapt2-3.2.1-4818971-linux.jar:f431b6f96c91a2c155144b091a9c97d9805c589fe8efc9c930b6cd346cb60a1e',
-        'com.android.tools.build:apksig:3.2.1:apksig-3.2.1.jar:2b46f2feffea66037aab29e4261b2433c190194a6ef97b958511eb157f2ccba5',
-        'com.android.tools.build:apkzlib:3.2.1:apkzlib-3.2.1.jar:c39ad0313905932431fe81c8899c2cf39a4d92ad6c4edcaa4b25432f461452aa',
-        'com.android.tools.build:builder-model:3.2.1:builder-model-3.2.1.jar:a9f68e6abcec122f9cb5ad352d3f05a3eb03acbcdca95e4d25c16310c2c965ff',
-        'com.android.tools.build:builder-test-api:3.2.1:builder-test-api-3.2.1.jar:533ac6c2b5884bb54967a33791f2628dfdfac7981af39417a333b43d4379b6be',
-        'com.android.tools.build:builder:3.2.1:builder-3.2.1.jar:aedcbfd115dbe91d09b4113e66ef50589b558d0aa3b2f133b1d867c9b87fae83',
-        'com.android.tools.build:gradle-api:3.2.1:gradle-api-3.2.1.jar:57cf0ac5ac1dca8afdb3f62b94265e776e7dcfa641cc3844fb53a05193de208d',
-        'com.android.tools.build:manifest-merger:26.2.1:manifest-merger-26.2.1.jar:8830573263361035d38cfdcb51e2db94029c93865b21334f5fbf8a27984281a6',
-        'com.android.tools.ddms:ddmlib:26.2.1:ddmlib-26.2.1.jar:a4bf0a29a19980bf27269465cc782064656750b77c26728f82f9e148b705218b',
-        'com.android.tools.external.com-intellij:intellij-core:26.2.1:intellij-core-26.2.1.jar:4925ad1892c2687cb1a63427d440ef519c8c59215fefe0dc5d541d5d411fcafe',
-        'com.android.tools.external.com-intellij:kotlin-compiler:26.2.1:kotlin-compiler-26.2.1.jar:daa064fd708f340ee25fb9823c4c74104ac77f1370b76d907eb9ae6daec0a2ae',
-        'com.android.tools.external.org-jetbrains:uast:26.2.1:uast-26.2.1.jar:f10f7258d2ab9189562cc0f9ad838c0378fdba439229173390a99de02ebac75b',
-        'com.android.tools.layoutlib:layoutlib-api:26.2.1:layoutlib-api-26.2.1.jar:ddbf4fca123733fa011595b1cc1f4ac2937ed327b60990711fafc33c775c2ade',
-        'com.android.tools.lint:lint-api:26.2.1:lint-api-26.2.1.jar:3b57e739de567b98bc9ab56c2c0ee66fc026b4adf5843e8f9804ca0666a6f66e',
-        'com.android.tools.lint:lint-checks:26.2.1:lint-checks-26.2.1.jar:c86f4cc9aaee722ee4ad70062f7b5af91e9b041914af27adc09f545ab0fb3bc6',
-        'com.android.tools.lint:lint-gradle-api:26.2.1:lint-gradle-api-26.2.1.jar:2283e7af32e301565f2a797e531f0fc8c648077d457afb3ffdddbee638976c2f',
-        'com.android.tools.lint:lint-gradle:26.2.1:lint-gradle-26.2.1.jar:8fd90b2f3ec788cbb9801c07ab3e1ea2255aa31a6093157d7ea0ff13d0315ecb',
-        'com.android.tools.lint:lint-kotlin:26.2.1:lint-kotlin-26.2.1.jar:7a6a5d2b18f69cf1b900d857c2632b4c683713c533295933b8b759f8cab4a877',
-        'com.android.tools.lint:lint:26.2.1:lint-26.2.1.jar:7848b82ae988b90dee259ae7c7e86e05cbf52db6cd21c8bbd38ce7df08f3f8c5',
-        'com.android.tools:annotations:26.2.1:annotations-26.2.1.jar:7391c6a1e080174b96e64ceb078dadd31ce4d8a2d2fee0ec65be202126f90f24',
-        'com.android.tools:common:26.2.1:common-26.2.1.jar:a50aab2d6411ff68f4004a87c7e93d87d8e980a0ec3b352246549897ea2d78e5',
-        'com.android.tools:dvlib:26.2.1:dvlib-26.2.1.jar:72a83bf2839b1df9b1fbf67ba45d1bfb9f966cd774da4320c762b2be8f1688aa',
-        'com.android.tools:repository:26.2.1:repository-26.2.1.jar:fa74dae09103faef703df38550ad8fa244c5b6d1bf90d6198be932292b3d9cc1',
-        'com.android.tools:sdk-common:26.2.1:sdk-common-26.2.1.jar:759d4b292ca69a35cf961fca377b54158fc6c88108978006999442e80a011cf4',
-        'com.android.tools:sdklib:26.2.1:sdklib-26.2.1.jar:248df7ad5eac4aeb6f96c394c76760de4b7b89ac056e54d0c21a739368b91b45',
+        'com.android.tools.analytics-library:protos:26.4.0:protos-26.4.0.jar:ad760915586797d39319f402837b378bff3bb4ed583e3e0c48c965631fb2135f',
+        'com.android.tools.analytics-library:shared:26.4.0:shared-26.4.0.jar:1332106a905d48909c81268c9e414946de3e83487db394c6073b0a9b5c3d0ed2',
+        'com.android.tools.analytics-library:tracker:26.4.0:tracker-26.4.0.jar:d0020cfbfd4cd75935f2972d6a24089840d4a10df6f3ef2a796093217dd37796',
+        'com.android.tools.build:apksig:3.4.0:apksig-3.4.0.jar:91d5a1866139c69756280355a6f61b4d619d0516841580114f45a10f2177327e',
+        'com.android.tools.build:apkzlib:3.4.0:apkzlib-3.4.0.jar:8653c85f5fdf1dde840e8b8af7396aeb79c34b66e541b5860059616006535592',
+        'com.android.tools.build:builder-model:3.4.0:builder-model-3.4.0.jar:a88f138124a9f016a70bcb4760359a502f65c7deed56507ee4014f4dd9ea853b',
+        'com.android.tools.build:builder-test-api:3.4.0:builder-test-api-3.4.0.jar:31089ab1ec19ca7687a010867d2f3807513c805b8226979706f4247b5d4df26f',
+        'com.android.tools.build:builder:3.4.0:builder-3.4.0.jar:476221b5203a7f50089bf185ed95000a34b6f5020ef0a17815afd58606922679',
+        'com.android.tools.build:gradle-api:3.4.0:gradle-api-3.4.0.jar:215eca38f6719213c2f492b4d622cdd11676c66c9871f8a2aed0c66d00175628',
+        'com.android.tools.build:manifest-merger:26.4.0:manifest-merger-26.4.0.jar:29e45e690dedd165035e97c21c2ca94d0bd4ec16b6b210daa26669a582b6f220',
+        'com.android.tools.ddms:ddmlib:26.4.0:ddmlib-26.4.0.jar:93f56fe4630c3166adbd6c51d7bb602d96abb91b07ba5b1165fdcd071e88c940',
+        'com.android.tools.external.com-intellij:intellij-core:26.4.0:intellij-core-26.4.0.jar:30cb0e879d4424de9677a50b537fb628636b4a50f5470af5e52437980c41421f',
+        'com.android.tools.external.com-intellij:kotlin-compiler:26.4.0:kotlin-compiler-26.4.0.jar:dd1fe225c31a0e012dc025336363a5b783e2c5c20ffb69e77f8f57e89420d998',
+        'com.android.tools.external.org-jetbrains:uast:26.4.0:uast-26.4.0.jar:f25f3285b775a983327583ff6584dea54e447813ef69e0ce08b05a45b5f4aab0',
+        'com.android.tools.layoutlib:layoutlib-api:26.4.0:layoutlib-api-26.4.0.jar:52128f5cf293b224072be361919bfd416e59480ab7264ddcdbbf046b0d7a12e3',
+        'com.android.tools.lint:lint-api:26.4.0:lint-api-26.4.0.jar:fdb8fca8ae4c254f438338d03d72605e00ed106f2d5550405af41ca1c8509401',
+        'com.android.tools.lint:lint-checks:26.4.0:lint-checks-26.4.0.jar:4ff52d40488cd3e22b9c6b2eb67784e0c3269d0b42ef9d17689cd75a7b2bceb4',
+        'com.android.tools.lint:lint-gradle-api:26.4.0:lint-gradle-api-26.4.0.jar:714b7a85c7d2aa10daeab16e969fe7530c659d0728a7f24021da456870418d0f',
+        'com.android.tools.lint:lint-gradle:26.4.0:lint-gradle-26.4.0.jar:b8c130d273f522388734457e1b96790f41528fcec6fda9e8eaa4e4d95a07cfbb',
+        'com.android.tools.lint:lint:26.4.0:lint-26.4.0.jar:83aa062fb0405b60ed358d858c8c2955e1bae44a455b498068c6a60988755f00',
+        'com.android.tools:annotations:26.4.0:annotations-26.4.0.jar:a7955b8e19c3a2a861d6faa43a58b7c0d46ea9112188ee3e235c6f9f439ecc1a',
+        'com.android.tools:common:26.4.0:common-26.4.0.jar:ea40b94b3c1284ea7700f011388e2906a8363a66abd902891722b3c557984852',
+        'com.android.tools:dvlib:26.4.0:dvlib-26.4.0.jar:23af89c535b01ba36ceed1b6b309b672814eba624e643cd7dedf0519edad50cc',
+        'com.android.tools:repository:26.4.0:repository-26.4.0.jar:3d1763ab46199374dc6d94129bba11c70f1d5857e2c81a3ac4898abca40b176b',
+        'com.android.tools:sdk-common:26.4.0:sdk-common-26.4.0.jar:78a522525b30ffc6b7bf1299c831d24ce385f68a9f4878f8f752e9baefa31b0f',
+        'com.android.tools:sdklib:26.4.0:sdklib-26.4.0.jar:b854c23892013a326d761cf071c72cf3e038ed0469d10f4a356829fa56e4c132',
         'com.google.code.findbugs:jsr305:1.3.9:jsr305-1.3.9.jar:905721a0eea90a81534abb7ee6ef4ea2e5e645fa1def0a5cd88402df1b46c9ed',
+        'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.code.gson:gson:2.8.0:gson-2.8.0.jar:c6221763bd79c4f1c3dc7f750b5f29a0bb38b367b81314c4f71896e340c40825',
-        'com.google.dagger:dagger-compiler:2.19:dagger-compiler-2.19.jar:27a4b202a2de908182edb261f8c0a264e08e5e4733d7514bc7fbf0d31da5c0fc',
-        'com.google.dagger:dagger-producers:2.19:dagger-producers-2.19.jar:a17663abe0fc38b676026950907d4c5f5e2bf338375415861eaff6e3bdb0b768',
-        'com.google.dagger:dagger-spi:2.19:dagger-spi-2.19.jar:e7a6379d82c841f6aac2866948ad1eed716528707814602842a8d844ce04e2e1',
-        'com.google.dagger:dagger:2.19:dagger-2.19.jar:514b6f1e0727c6572e1d65cb27e4ae668b7aeaeb93a29515182965265b609939',
-        'com.google.errorprone:error_prone_annotations:2.0.18:error_prone_annotations-2.0.18.jar:cb4cfad870bf563a07199f3ebea5763f0dec440fcda0b318640b1feaa788656b',
+        'com.google.dagger:dagger-compiler:2.22.1:dagger-compiler-2.22.1.jar:e5f28302cbe70a79d3620cddebfb8ec0736814f3980ffe1e673bfe3342f507d3',
+        'com.google.dagger:dagger-producers:2.22.1:dagger-producers-2.22.1.jar:f834a0082014213a68ff06a0f048d750178d02196c58b0b15beb367d32b97e35',
+        'com.google.dagger:dagger-spi:2.22.1:dagger-spi-2.22.1.jar:4b0b922793b3bcb91b99fabb75dba77c68afd7ae4c5f0c4fd6ba681f0a291c7d',
+        'com.google.dagger:dagger:2.22.1:dagger-2.22.1.jar:329d4340f24c4f5717af016c097e90668bfea2a5376e6aa9964b01cef3fd241a',
         'com.google.errorprone:error_prone_annotations:2.1.3:error_prone_annotations-2.1.3.jar:03d0329547c13da9e17c634d1049ea2ead093925e290567e1a364fd6b1fc7ff8',
         'com.google.errorprone:javac-shaded:9-dev-r4023-3:javac-shaded-9-dev-r4023-3.jar:65bfccf60986c47fbc17c9ebab0be626afc41741e0a6ec7109e0768817a36f30',
         'com.google.googlejavaformat:google-java-format:1.5:google-java-format-1.5.jar:aa19ad7850fb85178aa22f2fddb163b84d6ce4d0035872f30d4408195ca1144e',
-        'com.google.guava:guava:23.0:guava-23.0.jar:7baa80df284117e5b945b19b98d367a85ea7b7801bd358ff657946c3bd1b6596',
         'com.google.guava:guava:25.0-jre:guava-25.0-jre.jar:3fd4341776428c7e0e5c18a7c10de129475b69ab9d30aeafbb5c277bb6074fa9',
-        'com.google.j2objc:j2objc-annotations:1.1:j2objc-annotations-1.1.jar:40ceb7157feb263949e0f503fe5f71689333a621021aa20ce0d0acee3badaa0f',
+        'com.google.guava:guava:26.0-jre:guava-26.0-jre.jar:a0e9cabad665bc20bcd2b01f108e5fc03f756e13aea80abaadb9f407033bea2c',
+        'com.google.j2objc:j2objc-annotations:1.1:j2objc-annotations-1.1.jar:2994a7eb78f2710bd3d3bfb639b2c94e219cedac0d4d084d516e78c16dddecf6',
         'com.google.jimfs:jimfs:1.1:jimfs-1.1.jar:c4828e28d7c0a930af9387510b3bada7daa5c04d7c25a75c7b8b081f1c257ddd',
         'com.google.protobuf:protobuf-java:3.4.0:protobuf-java-3.4.0.jar:dce7e66b32456a1b1198da0caff3a8acb71548658391e798c79369241e6490a4',
         'com.googlecode.json-simple:json-simple:1.1:json-simple-1.1.jar:2d9484f4c649f708f47f9a479465fc729770ee65617dca3011836602264f6439',
@@ -50,7 +48,7 @@ dependencyVerification {
         'com.sun.activation:javax.activation:1.2.0:javax.activation-1.2.0.jar:993302b16cd7056f21e779cc577d175a810bb4900ef73cd8fbf2b50f928ba9ce',
         'com.sun.istack:istack-commons-runtime:2.21:istack-commons-runtime-2.21.jar:c33e67a0807095f02a0e2da139412dd7c4f9cc1a4c054b3e434f96831ba950f4',
         'com.sun.xml.fastinfoset:FastInfoset:1.2.13:FastInfoset-1.2.13.jar:27a77db909f3c2833c0b1a37c55af1db06045118ad2eed96ce567b6632bce038',
-        'commons-codec:commons-codec:1.9:commons-codec-1.9.jar:ad19d2601c3abf0b946b5c3a4113e226a8c1e3305e395b90013b78dd94a723ce',
+        'commons-codec:commons-codec:1.10:commons-codec-1.10.jar:4241dfa94e711d435f29a4604a3e2de5c4aa3c165e23bd066be6fc1fc4309569',
         'commons-logging:commons-logging:1.2:commons-logging-1.2.jar:daddea1ea0be0f56978ab3006b8ac92834afeefbd9b7e4e6316fca57df0fa636',
         'it.unimi.dsi:fastutil:7.2.0:fastutil-7.2.0.jar:74fa208043740642f7e6eb09faba15965218ad2f50ce3020efb100136e4b591c',
         'javax.annotation:jsr250-api:1.0:jsr250-api-1.0.jar:a1a922d0d9b6d183ed3800dfac01d1e1eb159f0e8c6f94736931c1def54a941f',
@@ -62,27 +60,28 @@ dependencyVerification {
         'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
         'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
         'org.apache.commons:commons-compress:1.12:commons-compress-1.12.jar:2c1542faf343185b7cab9c3d55c8ae5471d6d095d3887a4adefdbdf2984dc0b6',
-        'org.apache.httpcomponents:httpclient:4.5.2:httpclient-4.5.2.jar:0dffc621400d6c632f55787d996b8aeca36b30746a716e079a985f24d8074057',
-        'org.apache.httpcomponents:httpcore:4.4.5:httpcore-4.4.5.jar:64d5453874cab7e40a7065cb01a9a9ca1053845a9786b478878b679e0580cec3',
-        'org.apache.httpcomponents:httpmime:4.5.2:httpmime-4.5.2.jar:231a3f7e4962053db2be8461d5422e68fc458a3a7dd7d8ada803a348e21f8f07',
+        'org.apache.httpcomponents:httpclient:4.5.6:httpclient-4.5.6.jar:c03f813195e7a80e3608d0ddd8da80b21696a4c92a6a2298865bf149071551c7',
+        'org.apache.httpcomponents:httpcore:4.4.10:httpcore-4.4.10.jar:78ba1096561957db1b55200a159b648876430342d15d461277e62360da19f6fd',
+        'org.apache.httpcomponents:httpmime:4.5.6:httpmime-4.5.6.jar:0b2b1102c18d3c7e05a77214b9b7501a6f6056174ae5604e0e256776eda7553e',
         'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         'org.bouncycastle:bcpkix-jdk15on:1.56:bcpkix-jdk15on-1.56.jar:7043dee4e9e7175e93e0b36f45b1ec1ecb893c5f755667e8b916eb8dd201c6ca',
         'org.bouncycastle:bcprov-jdk15on:1.56:bcprov-jdk15on-1.56.jar:963e1ee14f808ffb99897d848ddcdb28fa91ddda867eb18d303e82728f878349',
-        'org.briarproject:obfs4proxy-android:0.0.7:obfs4proxy-android-0.0.7.zip:abdfb5d889d848de9bf214f9276abbf454808a505b870819eccc9a9e985bf617',
-        'org.briarproject:tor-android:0.3.4.8:tor-android-0.3.4.8.zip:989a0352d9d8d8172cd6c2137654e165e5d2beb10ed1211bab3814e224ad1926',
+        'org.briarproject:obfs4proxy-android:0.0.9:obfs4proxy-android-0.0.9.zip:9b7e9181535ea8d8bbe8ae6338e08cf4c5fc1e357a779393e0ce49586d459ae0',
+        'org.briarproject:tor-android:0.3.5.8:tor-android-0.3.5.8.zip:42a13a6f185be1a62f42e3f30ce66a3c099ac5ec890a65e7593111b65b44a54a',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
-        'org.codehaus.groovy:groovy-all:2.4.12:groovy-all-2.4.12.jar:6a56af4bd48903d56bec62821876cadefafd007360cc6bd0d8f7aa8d72b38be4',
+        'org.checkerframework:checker-qual:2.5.2:checker-qual-2.5.2.jar:64b02691c8b9d4e7700f8ee2e742dce7ea2c6e81e662b7522c9ee3bf568c040a',
+        'org.codehaus.groovy:groovy-all:2.4.15:groovy-all-2.4.15.jar:51d6c4e71782e85674239189499854359d380fb75e1a703756e3aaa5b98a5af0',
         'org.codehaus.mojo:animal-sniffer-annotations:1.14:animal-sniffer-annotations-1.14.jar:2068320bd6bad744c3673ab048f67e30bef8f518996fa380033556600669905d',
         'org.glassfish.jaxb:jaxb-core:2.2.11:jaxb-core-2.2.11.jar:37bcaee8ebb04362c8352a5bf6221b86967ecdab5164c696b10b9a2bb587b2aa',
         'org.glassfish.jaxb:jaxb-runtime:2.2.11:jaxb-runtime-2.2.11.jar:a874f2351cfba8e2946be3002d10c18a6da8f21b52ba2acf52f2b85d5520ed70',
         'org.glassfish.jaxb:txw2:2.2.11:txw2-2.2.11.jar:272a3ccad45a4511351920cd2a8633c53cab8d5220c7a92954da5526bb5eafea',
         'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
         'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
-        'org.jetbrains.kotlin:kotlin-reflect:1.2.0:kotlin-reflect-1.2.0.jar:4f48a872bad6e4d9c053f4ad610d11e4012ad7e58dc19a03dd5eb811f36069dd',
-        'org.jetbrains.kotlin:kotlin-stdlib-common:1.2.71:kotlin-stdlib-common-1.2.71.jar:63999687ff2fce8a592dd180ffbbf8f1d21c26b4044c55cdc74ff3cf3b3cf328',
-        'org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.2.71:kotlin-stdlib-jdk7-1.2.71.jar:b136bd61b240e07d4d92ce00d3bd1dbf584400a7bf5f220c2f3cd22446858082',
-        'org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.2.71:kotlin-stdlib-jdk8-1.2.71.jar:ac3c8abf47790b64b4f7e2509a53f0c145e061ac1612a597520535d199946ea9',
-        'org.jetbrains.kotlin:kotlin-stdlib:1.2.71:kotlin-stdlib-1.2.71.jar:4c895c270b87f5fec2a2796e1d89c15407ee821de961527c28588bb46afbc68b',
+        'org.jetbrains.kotlin:kotlin-reflect:1.3.21:kotlin-reflect-1.3.21.jar:a3065c822633191e0a3e3ee12a29bec234fc4b2864a6bb87ef48cce3e9e0c26a',
+        'org.jetbrains.kotlin:kotlin-stdlib-common:1.3.21:kotlin-stdlib-common-1.3.21.jar:cea61f7b611895e64f58569a9757fc0ab0d582f107211e1930e0ce2a0add52a7',
+        'org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.21:kotlin-stdlib-jdk7-1.3.21.jar:a87875604fd42140da6938ae4d35ee61081f4482536efc6d2615b8b626a198af',
+        'org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.3.21:kotlin-stdlib-jdk8-1.3.21.jar:5823ed66ac122a1c55442ebca5a209a843ccd87f562edc31a787f3d2e47f74d4',
+        'org.jetbrains.kotlin:kotlin-stdlib:1.3.21:kotlin-stdlib-1.3.21.jar:38ba2370d9f06f50433e06b2ca775b94473c2e2785f410926079ab793c72b034',
         'org.jetbrains.trove4j:trove4j:20160824:trove4j-20160824.jar:1917871c8deb468307a584680c87a44572f5a8b0b98c6d397fc0f5f86596dbe7',
         'org.jetbrains:annotations:13.0:annotations-13.0.jar:ace2a10dc8e2d5fd34925ecac03e4988b2c0f851650c94b8cef49ba1bd111478',
         'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',

bramble-api/build.gradle

@@ -7,7 +7,7 @@ apply plugin: 'witness'
 apply from: 'witness.gradle'
 
 dependencies {
-	implementation "com.google.dagger:dagger:2.19"
+	implementation "com.google.dagger:dagger:2.22.1"
 	implementation 'com.google.code.findbugs:jsr305:3.0.2'
 
 	testImplementation 'junit:junit:4.12'

bramble-api/src/main/java/org/briarproject/bramble/api/UnsupportedVersionException.java

@@ -0,0 +1,18 @@
+package org.briarproject.bramble.api;
+
+/**
+ * Thrown when data being parsed uses a protocol or format version that is not
+ * supported.
+ */
+public class UnsupportedVersionException extends FormatException {
+
+	private final boolean tooOld;
+
+	public UnsupportedVersionException(boolean tooOld) {
+		this.tooOld = tooOld;
+	}
+
+	public boolean isTooOld() {
+		return tooOld;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/client/BdfIncomingMessageHook.java

@@ -33,7 +33,8 @@ public abstract class BdfIncomingMessageHook implements IncomingMessageHook {
 	/**
 	 * Called once for each incoming message that passes validation.
 	 *
-	 * @return whether or not this message should be shared
+	 * @param txn A read-write transaction
+	 * @return Whether or not this message should be shared
 	 * @throws DbException Should only be used for real database errors.
 	 * If this is thrown, delivery will be attempted again at next startup,
 	 * whereas if a FormatException is thrown, the message will be permanently

bramble-api/src/main/java/org/briarproject/bramble/api/contact/Contact.java

@@ -8,6 +8,7 @@ import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
+import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_PUBLIC_KEY_LENGTH;
 import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 @Immutable
@@ -19,21 +20,28 @@ public class Contact {
 	private final AuthorId localAuthorId;
 	@Nullable
 	private final String alias;
-	private final boolean verified, active;
+	@Nullable
+	private final byte[] handshakePublicKey;
+	private final boolean verified;
 
 	public Contact(ContactId id, Author author, AuthorId localAuthorId,
-			@Nullable String alias, boolean verified, boolean active) {
+			@Nullable String alias, @Nullable byte[] handshakePublicKey,
+			boolean verified) {
 		if (alias != null) {
 			int aliasLength = toUtf8(alias).length;
 			if (aliasLength == 0 || aliasLength > MAX_AUTHOR_NAME_LENGTH)
 				throw new IllegalArgumentException();
 		}
+		if (handshakePublicKey != null && (handshakePublicKey.length == 0 ||
+				handshakePublicKey.length > MAX_PUBLIC_KEY_LENGTH)) {
+			throw new IllegalArgumentException();
+		}
 		this.id = id;
 		this.author = author;
 		this.localAuthorId = localAuthorId;
 		this.alias = alias;
+		this.handshakePublicKey = handshakePublicKey;
 		this.verified = verified;
-		this.active = active;
 	}
 
 	public ContactId getId() {
@@ -53,12 +61,13 @@ public class Contact {
 		return alias;
 	}
 
-	public boolean isVerified() {
-		return verified;
+	@Nullable
+	public byte[] getHandshakePublicKey() {
+		return handshakePublicKey;
 	}
 
-	public boolean isActive() {
-		return active;
+	public boolean isVerified() {
+		return verified;
 	}
 
 	@Override

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactExchangeListener.java

@@ -1,20 +0,0 @@
-package org.briarproject.bramble.api.contact;
-
-import org.briarproject.bramble.api.identity.Author;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-@NotNullByDefault
-public interface ContactExchangeListener {
-
-	void contactExchangeSucceeded(Author remoteAuthor);
-
-	/**
-	 * The exchange failed because the contact already exists.
-	 */
-	void duplicateContact(Author remoteAuthor);
-
-	/**
-	 * A general failure.
-	 */
-	void contactExchangeFailed();
-}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactExchangeTask.java

@@ -18,31 +18,30 @@ public interface ContactExchangeTask {
 	byte PROTOCOL_VERSION = 1;
 
 	/**
-	 * Label for deriving Alice's header key from the master secret.
+	 * Label for deriving Alice's header key from the master key.
 	 */
 	String ALICE_KEY_LABEL =
 			"org.briarproject.bramble.contact/ALICE_HEADER_KEY";
 
 	/**
-	 * Label for deriving Bob's header key from the master secret.
+	 * Label for deriving Bob's header key from the master key.
 	 */
 	String BOB_KEY_LABEL = "org.briarproject.bramble.contact/BOB_HEADER_KEY";
 
 	/**
-	 * Label for deriving Alice's key binding nonce from the master secret.
+	 * Label for deriving Alice's key binding nonce from the master key.
 	 */
 	String ALICE_NONCE_LABEL = "org.briarproject.bramble.contact/ALICE_NONCE";
 
 	/**
-	 * Label for deriving Bob's key binding nonce from the master secret.
+	 * Label for deriving Bob's key binding nonce from the master key.
 	 */
 	String BOB_NONCE_LABEL = "org.briarproject.bramble.contact/BOB_NONCE";
 
 	/**
 	 * Exchanges contact information with a remote peer.
 	 */
-	void startExchange(ContactExchangeListener listener,
-			LocalAuthor localAuthor, SecretKey masterSecret,
+	void startExchange(LocalAuthor localAuthor, SecretKey masterKey,
 			DuplexTransportConnection conn, TransportId transportId,
 			boolean alice);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactManager.java

@@ -1,7 +1,10 @@
 package org.briarproject.bramble.api.contact;
 
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.UnsupportedVersionException;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.NoSuchContactException;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorId;
@@ -31,7 +34,7 @@ public interface ContactManager {
 	 * @param alice true if the local party is Alice
 	 */
 	ContactId addContact(Transaction txn, Author remote, AuthorId local,
-			SecretKey master, long timestamp, boolean alice, boolean verified,
+			SecretKey rootKey, long timestamp, boolean alice, boolean verified,
 			boolean active) throws DbException;
 
 	/**
@@ -39,7 +42,7 @@ public interface ContactManager {
 	 * and returns an ID for the contact.
 	 */
 	ContactId addContact(Transaction txn, Author remote, AuthorId local,
-			boolean verified, boolean active) throws DbException;
+			boolean verified) throws DbException;
 
 	/**
 	 * Stores a contact associated with the given local and remote pseudonyms,
@@ -48,10 +51,40 @@ public interface ContactManager {
 	 *
 	 * @param alice true if the local party is Alice
 	 */
-	ContactId addContact(Author remote, AuthorId local, SecretKey master,
+	ContactId addContact(Author remote, AuthorId local, SecretKey rootKey,
 			long timestamp, boolean alice, boolean verified, boolean active)
 			throws DbException;
 
+	/**
+	 * Returns the handshake link that needs to be sent to a contact we want
+	 * to add.
+	 */
+	String getHandshakeLink() throws DbException;
+
+	/**
+	 * Creates a {@link PendingContact} from the given handshake link and
+	 * alias, adds it to the database and returns it.
+	 *
+	 * @param link The handshake link received from the contact we want to add
+	 * @param alias The alias the user has given this contact
+	 * @return A PendingContact representing the contact to be added
+	 * @throws UnsupportedVersionException If the link uses a format version
+	 * that is not supported
+	 * @throws FormatException If the link is invalid
+	 */
+	PendingContact addPendingContact(String link, String alias)
+			throws DbException, FormatException;
+
+	/**
+	 * Returns a list of {@link PendingContact}s.
+	 */
+	Collection<PendingContact> getPendingContacts() throws DbException;
+
+	/**
+	 * Removes a {@link PendingContact}.
+	 */
+	void removePendingContact(PendingContactId p) throws DbException;
+
 	/**
 	 * Returns the contact with the given ID.
 	 */
@@ -61,7 +94,7 @@ public interface ContactManager {
 	 * Returns the contact with the given remoteAuthorId
 	 * that was added by the LocalAuthor with the given localAuthorId
 	 *
-	 * @throws org.briarproject.bramble.api.db.NoSuchContactException
+	 * @throws NoSuchContactException If the contact is not in the database
 	 */
 	Contact getContact(AuthorId remoteAuthorId, AuthorId localAuthorId)
 			throws DbException;
@@ -70,7 +103,7 @@ public interface ContactManager {
 	 * Returns the contact with the given remoteAuthorId
 	 * that was added by the LocalAuthor with the given localAuthorId
 	 *
-	 * @throws org.briarproject.bramble.api.db.NoSuchContactException
+	 * @throws NoSuchContactException If the contact is not in the database
 	 */
 	Contact getContact(Transaction txn, AuthorId remoteAuthorId,
 			AuthorId localAuthorId) throws DbException;
@@ -78,7 +111,7 @@ public interface ContactManager {
 	/**
 	 * Returns all active contacts.
 	 */
-	Collection<Contact> getActiveContacts() throws DbException;
+	Collection<Contact> getContacts() throws DbException;
 
 	/**
 	 * Removes a contact and all associated state.
@@ -90,12 +123,6 @@ public interface ContactManager {
 	 */
 	void removeContact(Transaction txn, ContactId c) throws DbException;
 
-	/**
-	 * Marks a contact as active or inactive.
-	 */
-	void setContactActive(Transaction txn, ContactId c, boolean active)
-			throws DbException;
-
 	/**
 	 * Sets an alias name for the contact or unsets it if alias is null.
 	 */
@@ -132,8 +159,20 @@ public interface ContactManager {
 
 	interface ContactHook {
 
+		/**
+		 * Called when a contact is being added.
+		 *
+		 * @param txn A read-write transaction
+		 * @param c The contact that is being added
+		 */
 		void addingContact(Transaction txn, Contact c) throws DbException;
 
+		/**
+		 * Called when a contact is being removed
+		 *
+		 * @param txn A read-write transaction
+		 * @param c The contact that is being removed
+		 */
 		void removingContact(Transaction txn, Contact c) throws DbException;
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/contact/HandshakeLinkConstants.java

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.api.contact;
+
+import java.util.regex.Pattern;
+
+public interface HandshakeLinkConstants {
+
+	/**
+	 * The current version of the handshake link format.
+	 */
+	int FORMAT_VERSION = 0;
+
+	/**
+	 * The length of a base32-encoded handshake link in bytes, excluding the
+	 * 'briar://' prefix.
+	 */
+	int BASE32_LINK_BYTES = 53;
+
+	/**
+	 * The length of a raw handshake link in bytes, before base32 encoding.
+	 */
+	int RAW_LINK_BYTES = 33;
+
+	/**
+	 * Regular expression for matching handshake links, including or excluding
+	 * the 'briar://' prefix.
+	 */
+	Pattern LINK_REGEX =
+			Pattern.compile("(briar://)?([a-z2-7]{" + BASE32_LINK_BYTES + "})");
+
+	/**
+	 * Label for hashing handshake public keys to calculate their identifiers.
+	 */
+	String ID_LABEL = "org.briarproject.bramble/HANDSHAKE_KEY_ID";
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/PendingContact.java

@@ -0,0 +1,56 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class PendingContact {
+
+	private final PendingContactId id;
+	private final byte[] publicKey;
+	private final String alias;
+	private final PendingContactState state;
+	private final long timestamp;
+
+	public PendingContact(PendingContactId id, byte[] publicKey,
+			String alias, PendingContactState state, long timestamp) {
+		this.id = id;
+		this.publicKey = publicKey;
+		this.alias = alias;
+		this.state = state;
+		this.timestamp = timestamp;
+	}
+
+	public PendingContactId getId() {
+		return id;
+	}
+
+	public byte[] getPublicKey() {
+		return publicKey;
+	}
+
+	public String getAlias() {
+		return alias;
+	}
+
+	public PendingContactState getState() {
+		return state;
+	}
+
+	public long getTimestamp() {
+		return timestamp;
+	}
+
+	@Override
+	public int hashCode() {
+		return id.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof PendingContact &&
+				id.equals(((PendingContact) o).id);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/PendingContactId.java

@@ -0,0 +1,25 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.UniqueId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * Type-safe wrapper for a byte array that uniquely identifies a
+ * {@link PendingContact}.
+ */
+@ThreadSafe
+@NotNullByDefault
+public class PendingContactId extends UniqueId {
+
+	public PendingContactId(byte[] id) {
+		super(id);
+	}
+
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof PendingContactId && super.equals(o);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/PendingContactState.java

@@ -0,0 +1,30 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public enum PendingContactState {
+
+	WAITING_FOR_CONNECTION(0),
+	CONNECTED(1),
+	ADDING_CONTACT(2),
+	FAILED(3);
+
+	private final int value;
+
+	PendingContactState(int value) {
+		this.value = value;
+	}
+
+	public int getValue() {
+		return value;
+	}
+
+	public static PendingContactState fromValue(int value) {
+		for (PendingContactState s : values()) if (s.value == value) return s;
+		throw new IllegalArgumentException();
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/ContactAddedEvent.java

@@ -14,18 +14,12 @@ import javax.annotation.concurrent.Immutable;
 public class ContactAddedEvent extends Event {
 
 	private final ContactId contactId;
-	private final boolean active;
 
-	public ContactAddedEvent(ContactId contactId, boolean active) {
+	public ContactAddedEvent(ContactId contactId) {
 		this.contactId = contactId;
-		this.active = active;
 	}
 
 	public ContactId getContactId() {
 		return contactId;
 	}
-
-	public boolean isActive() {
-		return active;
-	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/ContactAddedRemotelyEvent.java

@@ -1,4 +1,4 @@
-package org.briarproject.briar.api.introduction.event;
+package org.briarproject.bramble.api.contact.event;
 
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.event.Event;
@@ -8,11 +8,11 @@ import javax.annotation.concurrent.Immutable;
 
 @Immutable
 @NotNullByDefault
-public class IntroductionSucceededEvent extends Event {
+public class ContactAddedRemotelyEvent extends Event {
 
 	private final Contact contact;
 
-	public IntroductionSucceededEvent(Contact contact) {
+	public ContactAddedRemotelyEvent(Contact contact) {
 		this.contact = contact;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/ContactExchangeFailedEvent.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.api.contact.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public class ContactExchangeFailedEvent extends Event {
+
+	@Nullable
+	private final Author duplicateRemoteAuthor;
+
+	public ContactExchangeFailedEvent(@Nullable Author duplicateRemoteAuthor) {
+		this.duplicateRemoteAuthor = duplicateRemoteAuthor;
+	}
+
+	public ContactExchangeFailedEvent() {
+		this(null);
+	}
+
+	@Nullable
+	public Author getDuplicateRemoteAuthor() {
+		return duplicateRemoteAuthor;
+	}
+
+	public boolean wasDuplicateContact() {
+		return duplicateRemoteAuthor != null;
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/ContactExchangeSucceededEvent.java

@@ -0,0 +1,20 @@
+package org.briarproject.bramble.api.contact.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public class ContactExchangeSucceededEvent extends Event {
+
+	private final Author remoteAuthor;
+
+	public ContactExchangeSucceededEvent(Author remoteAuthor) {
+		this.remoteAuthor = remoteAuthor;
+	}
+
+	public Author getRemoteAuthor() {
+		return remoteAuthor;
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/ContactStatusChangedEvent.java

@@ -1,31 +0,0 @@
-package org.briarproject.bramble.api.contact.event;
-
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import javax.annotation.concurrent.Immutable;
-
-/**
- * An event that is broadcast when a contact is marked active or inactive.
- */
-@Immutable
-@NotNullByDefault
-public class ContactStatusChangedEvent extends Event {
-
-	private final ContactId contactId;
-	private final boolean active;
-
-	public ContactStatusChangedEvent(ContactId contactId, boolean active) {
-		this.contactId = contactId;
-		this.active = active;
-	}
-
-	public ContactId getContactId() {
-		return contactId;
-	}
-
-	public boolean isActive() {
-		return active;
-	}
-}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/PendingContactRemovedEvent.java

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api.contact.event;
+
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a pending contact is removed.
+ */
+@Immutable
+@NotNullByDefault
+public class PendingContactRemovedEvent extends Event {
+
+	private final PendingContactId id;
+
+	public PendingContactRemovedEvent(PendingContactId id) {
+		this.id = id;
+	}
+
+	public PendingContactId getId() {
+		return id;
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/PendingContactStateChangedEvent.java

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.api.contact.event;
+
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.contact.PendingContactState;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a pending contact's state is changed.
+ */
+@Immutable
+@NotNullByDefault
+public class PendingContactStateChangedEvent extends Event {
+
+	private final PendingContactId id;
+	private final PendingContactState state;
+
+	public PendingContactStateChangedEvent(PendingContactId id,
+			PendingContactState state) {
+		this.id = id;
+		this.state = state;
+	}
+
+	public PendingContactId getId() {
+		return id;
+	}
+
+	public PendingContactState getPendingContactState() {
+		return state;
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/crypto/KeyAgreementCrypto.java

@@ -2,7 +2,7 @@ package org.briarproject.bramble.api.crypto;
 
 /**
  * Crypto operations for the key agreement protocol - see
- * https://code.briarproject.org/akwizgran/briar-spec/blob/master/protocols/BQP.md
+ * https://code.briarproject.org/briar/briar-spec/blob/master/protocols/BQP.md
  */
 public interface KeyAgreementCrypto {
 

bramble-api/src/main/java/org/briarproject/bramble/api/crypto/TransportCrypto.java

@@ -1,29 +1,45 @@
 package org.briarproject.bramble.api.crypto;
 
 import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.transport.HandshakeKeys;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 /**
  * Crypto operations for the transport security protocol - see
- * https://code.briarproject.org/akwizgran/briar-spec/blob/master/protocols/BTP.md
+ * https://code.briarproject.org/briar/briar-spec/blob/master/protocols/BTP.md
  */
 public interface TransportCrypto {
 
 	/**
 	 * Derives initial transport keys for the given transport in the given
-	 * rotation period from the given master secret.
+	 * time period from the given root key.
 	 *
 	 * @param alice whether the keys are for use by Alice or Bob.
 	 * @param active whether the keys are usable for outgoing streams.
 	 */
-	TransportKeys deriveTransportKeys(TransportId t, SecretKey master,
-			long rotationPeriod, boolean alice, boolean active);
+	TransportKeys deriveTransportKeys(TransportId t, SecretKey rootKey,
+			long timePeriod, boolean alice, boolean active);
 
 	/**
-	 * Rotates the given transport keys to the given rotation period. If the
-	 * keys are for the given period or any later period they are not rotated.
+	 * Rotates the given transport keys to the given time period. If the keys
+	 * are for the given period or any later period they are not rotated.
 	 */
-	TransportKeys rotateTransportKeys(TransportKeys k, long rotationPeriod);
+	TransportKeys rotateTransportKeys(TransportKeys k, long timePeriod);
+
+	/**
+	 * Derives handshake keys for the given transport in the given time period
+	 * from the given root key.
+	 *
+	 * @param alice whether the keys are for use by Alice or Bob.
+	 */
+	HandshakeKeys deriveHandshakeKeys(TransportId t, SecretKey rootKey,
+			long timePeriod, boolean alice);
+
+	/**
+	 * Updates the given handshake keys to the given time period. If the keys
+	 * are for the given period or any later period they are not updated.
+	 */
+	HandshakeKeys updateHandshakeKeys(HandshakeKeys k, long timePeriod);
 
 	/**
 	 * Encodes the pseudo-random tag that is used to recognise a stream.

bramble-api/src/main/java/org/briarproject/bramble/api/db/CommitAction.java

@@ -0,0 +1,20 @@
+package org.briarproject.bramble.api.db;
+
+import org.briarproject.bramble.api.event.EventExecutor;
+
+/**
+ * An action that's taken when a {@link Transaction} is committed.
+ */
+public interface CommitAction {
+
+	void accept(Visitor visitor);
+
+	interface Visitor {
+
+		@EventExecutor
+		void visit(EventAction a);
+
+		@EventExecutor
+		void visit(TaskAction a);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -2,10 +2,12 @@ package org.briarproject.bramble.api.db;
 
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorId;
-import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.identity.Identity;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.settings.Settings;
@@ -20,8 +22,11 @@ import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.validation.MessageState;
-import org.briarproject.bramble.api.transport.KeySet;
-import org.briarproject.bramble.api.transport.KeySetId;
+import org.briarproject.bramble.api.transport.HandshakeKeySet;
+import org.briarproject.bramble.api.transport.HandshakeKeySetId;
+import org.briarproject.bramble.api.transport.HandshakeKeys;
+import org.briarproject.bramble.api.transport.TransportKeySet;
+import org.briarproject.bramble.api.transport.TransportKeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.Collection;
@@ -101,7 +106,7 @@ public interface DatabaseComponent {
 	 * and returns an ID for the contact.
 	 */
 	ContactId addContact(Transaction txn, Author remote, AuthorId local,
-			boolean verified, boolean active) throws DbException;
+			boolean verified) throws DbException;
 
 	/**
 	 * Stores a group.
@@ -109,9 +114,23 @@ public interface DatabaseComponent {
 	void addGroup(Transaction txn, Group g) throws DbException;
 
 	/**
-	 * Stores a local pseudonym.
+	 * Stores the given handshake keys for the given contact and returns a
+	 * key set ID.
 	 */
-	void addLocalAuthor(Transaction txn, LocalAuthor a) throws DbException;
+	HandshakeKeySetId addHandshakeKeys(Transaction txn, ContactId c,
+			HandshakeKeys k) throws DbException;
+
+	/**
+	 * Stores the given handshake keys for the given pending contact and
+	 * returns a key set ID.
+	 */
+	HandshakeKeySetId addHandshakeKeys(Transaction txn, PendingContactId p,
+			HandshakeKeys k) throws DbException;
+
+	/**
+	 * Stores an identity.
+	 */
+	void addIdentity(Transaction txn, Identity i) throws DbException;
 
 	/**
 	 * Stores a local message.
@@ -119,6 +138,12 @@ public interface DatabaseComponent {
 	void addLocalMessage(Transaction txn, Message m, Metadata meta,
 			boolean shared) throws DbException;
 
+	/**
+	 * Stores a pending contact.
+	 */
+	void addPendingContact(Transaction txn, PendingContact p)
+			throws DbException;
+
 	/**
 	 * Stores a transport.
 	 */
@@ -129,25 +154,39 @@ public interface DatabaseComponent {
 	 * Stores the given transport keys for the given contact and returns a
 	 * key set ID.
 	 */
-	KeySetId addTransportKeys(Transaction txn, ContactId c,
+	TransportKeySetId addTransportKeys(Transaction txn, ContactId c,
 			TransportKeys k) throws DbException;
 
 	/**
 	 * Returns true if the database contains the given contact for the given
 	 * local pseudonym.
+	 * <p/>
+	 * Read-only.
 	 */
 	boolean containsContact(Transaction txn, AuthorId remote, AuthorId local)
 			throws DbException;
 
 	/**
 	 * Returns true if the database contains the given group.
+	 * <p/>
+	 * Read-only.
 	 */
 	boolean containsGroup(Transaction txn, GroupId g) throws DbException;
 
 	/**
-	 * Returns true if the database contains the given local author.
+	 * Returns true if the database contains an identity for the given
+	 * pseudonym.
+	 * <p/>
+	 * Read-only.
 	 */
-	boolean containsLocalAuthor(Transaction txn, AuthorId local)
+	boolean containsIdentity(Transaction txn, AuthorId a) throws DbException;
+
+	/**
+	 * Returns true if the database contains the given pending contact.
+	 * <p/>
+	 * Read-only.
+	 */
+	boolean containsPendingContact(Transaction txn, PendingContactId p)
 			throws DbException;
 
 	/**
@@ -270,18 +309,26 @@ public interface DatabaseComponent {
 			throws DbException;
 
 	/**
-	 * Returns the local pseudonym with the given ID.
+	 * Returns all handshake keys for the given transport.
 	 * <p/>
 	 * Read-only.
 	 */
-	LocalAuthor getLocalAuthor(Transaction txn, AuthorId a) throws DbException;
+	Collection<HandshakeKeySet> getHandshakeKeys(Transaction txn, TransportId t)
+			throws DbException;
 
 	/**
-	 * Returns all local pseudonyms.
+	 * Returns the identity for the local pseudonym with the given ID.
 	 * <p/>
 	 * Read-only.
 	 */
-	Collection<LocalAuthor> getLocalAuthors(Transaction txn) throws DbException;
+	Identity getIdentity(Transaction txn, AuthorId a) throws DbException;
+
+	/**
+	 * Returns the identities for all local pseudonyms.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<Identity> getIdentities(Transaction txn) throws DbException;
 
 	/**
 	 * Returns the message with the given ID.
@@ -417,6 +464,14 @@ public interface DatabaseComponent {
 	 */
 	long getNextSendTime(Transaction txn, ContactId c) throws DbException;
 
+	/**
+	 * Returns all pending contacts.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<PendingContact> getPendingContacts(Transaction txn)
+			throws DbException;
+
 	/**
 	 * Returns all settings in the given namespace.
 	 * <p/>
@@ -429,14 +484,20 @@ public interface DatabaseComponent {
 	 * <p/>
 	 * Read-only.
 	 */
-	Collection<KeySet> getTransportKeys(Transaction txn, TransportId t)
+	Collection<TransportKeySet> getTransportKeys(Transaction txn, TransportId t)
 			throws DbException;
 
+	/**
+	 * Increments the outgoing stream counter for the given handshake keys.
+	 */
+	void incrementStreamCounter(Transaction txn, TransportId t,
+			HandshakeKeySetId k) throws DbException;
+
 	/**
 	 * Increments the outgoing stream counter for the given transport keys.
 	 */
-	void incrementStreamCounter(Transaction txn, TransportId t, KeySetId k)
-			throws DbException;
+	void incrementStreamCounter(Transaction txn, TransportId t,
+			TransportKeySetId k) throws DbException;
 
 	/**
 	 * Merges the given metadata with the existing metadata for the given
@@ -492,15 +553,27 @@ public interface DatabaseComponent {
 	void removeGroup(Transaction txn, Group g) throws DbException;
 
 	/**
-	 * Removes a local pseudonym (and all associated state) from the database.
+	 * Removes the given handshake keys from the database.
 	 */
-	void removeLocalAuthor(Transaction txn, AuthorId a) throws DbException;
+	void removeHandshakeKeys(Transaction txn, TransportId t,
+			HandshakeKeySetId k) throws DbException;
+
+	/**
+	 * Removes an identity (and all associated state) from the database.
+	 */
+	void removeIdentity(Transaction txn, AuthorId a) throws DbException;
 
 	/**
 	 * Removes a message (and all associated state) from the database.
 	 */
 	void removeMessage(Transaction txn, MessageId m) throws DbException;
 
+	/**
+	 * Removes a pending contact (and all associated state) from the database.
+	 */
+	void removePendingContact(Transaction txn, PendingContactId p)
+			throws DbException;
+
 	/**
 	 * Removes a transport (and all associated state) from the database.
 	 */
@@ -509,20 +582,14 @@ public interface DatabaseComponent {
 	/**
 	 * Removes the given transport keys from the database.
 	 */
-	void removeTransportKeys(Transaction txn, TransportId t, KeySetId k)
-			throws DbException;
+	void removeTransportKeys(Transaction txn, TransportId t,
+			TransportKeySetId k) throws DbException;
 
 	/**
 	 * Marks the given contact as verified.
 	 */
 	void setContactVerified(Transaction txn, ContactId c) throws DbException;
 
-	/**
-	 * Marks the given contact as active or inactive.
-	 */
-	void setContactActive(Transaction txn, ContactId c, boolean active)
-			throws DbException;
-
 	/**
 	 * Sets an alias name for the contact or unsets it if alias is null.
 	 */
@@ -553,21 +620,42 @@ public interface DatabaseComponent {
 			Collection<MessageId> dependencies) throws DbException;
 
 	/**
-	 * Sets the reordering window for the given key set and transport in the
-	 * given rotation period.
+	 * Sets the handshake key pair for the identity with the given ID.
 	 */
-	void setReorderingWindow(Transaction txn, KeySetId k, TransportId t,
-			long rotationPeriod, long base, byte[] bitmap) throws DbException;
+	void setHandshakeKeyPair(Transaction txn, AuthorId local, byte[] publicKey,
+			byte[] privateKey) throws DbException;
+
+	/**
+	 * Sets the reordering window for the given transport key set in the given
+	 * time period.
+	 */
+	void setReorderingWindow(Transaction txn, TransportKeySetId k,
+			TransportId t, long timePeriod, long base, byte[] bitmap)
+			throws DbException;
+
+	/**
+	 * Sets the reordering window for the given handshake key set in the given
+	 * time period.
+	 */
+	void setReorderingWindow(Transaction txn, HandshakeKeySetId k,
+			TransportId t, long timePeriod, long base, byte[] bitmap)
+			throws DbException;
 
 	/**
 	 * Marks the given transport keys as usable for outgoing streams.
 	 */
-	void setTransportKeysActive(Transaction txn, TransportId t, KeySetId k)
+	void setTransportKeysActive(Transaction txn, TransportId t,
+			TransportKeySetId k) throws DbException;
+
+	/**
+	 * Stores the given handshake keys, deleting any keys they have replaced.
+	 */
+	void updateHandshakeKeys(Transaction txn, Collection<HandshakeKeySet> keys)
 			throws DbException;
 
 	/**
 	 * Stores the given transport keys, deleting any keys they have replaced.
 	 */
-	void updateTransportKeys(Transaction txn, Collection<KeySet> keys)
+	void updateTransportKeys(Transaction txn, Collection<TransportKeySet> keys)
 			throws DbException;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseConfig.java

@@ -10,6 +10,4 @@ public interface DatabaseConfig {
 	File getDatabaseDirectory();
 
 	File getDatabaseKeyDirectory();
-
-	long getMaxSize();
 }

bramble-api/src/main/java/org/briarproject/bramble/api/db/EventAction.java

@@ -0,0 +1,24 @@
+package org.briarproject.bramble.api.db;
+
+import org.briarproject.bramble.api.event.Event;
+
+/**
+ * A {@link CommitAction} that broadcasts an event.
+ */
+public class EventAction implements CommitAction {
+
+	private final Event event;
+
+	EventAction(Event event) {
+		this.event = event;
+	}
+
+	public Event getEvent() {
+		return event;
+	}
+
+	@Override
+	public void accept(Visitor visitor) {
+		visitor.visit(this);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/db/NoSuchIdentityException.java

@@ -1,9 +1,9 @@
 package org.briarproject.bramble.api.db;
 
 /**
- * Thrown when a database operation is attempted for a pseudonym that is not in
+ * Thrown when a database operation is attempted for an identity that is not in
  * the database. This exception may occur due to concurrent updates and does
  * not indicate a database error.
  */
-public class NoSuchLocalAuthorException extends DbException {
+public class NoSuchIdentityException extends DbException {
 }

bramble-api/src/main/java/org/briarproject/bramble/api/db/NoSuchPendingContactException.java

@@ -0,0 +1,9 @@
+package org.briarproject.bramble.api.db;
+
+/**
+ * Thrown when a database operation is attempted for a pending contact that is
+ * not in the database. This exception may occur due to concurrent updates and
+ * does not indicate a database error.
+ */
+public class NoSuchPendingContactException extends DbException {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/db/PendingContactExistsException.java

@@ -0,0 +1,9 @@
+package org.briarproject.bramble.api.db;
+
+/**
+ * Thrown when a duplicate pending contact is added to the database. This
+ * exception may occur due to concurrent updates and does not indicate a
+ * database error.
+ */
+public class PendingContactExistsException extends DbException {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/db/TaskAction.java

@@ -0,0 +1,24 @@
+package org.briarproject.bramble.api.db;
+
+import org.briarproject.bramble.api.event.EventExecutor;
+
+/**
+ * A {@link CommitAction} that submits a task to the {@link EventExecutor}.
+ */
+public class TaskAction implements CommitAction {
+
+	private final Runnable task;
+
+	TaskAction(Runnable task) {
+		this.task = task;
+	}
+
+	public Runnable getTask() {
+		return task;
+	}
+
+	@Override
+	public void accept(Visitor visitor) {
+		visitor.visit(this);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/db/Transaction.java

@@ -1,13 +1,15 @@
 package org.briarproject.bramble.api.db;
 
 import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventExecutor;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import javax.annotation.concurrent.NotThreadSafe;
 
+import static java.util.Collections.emptyList;
+
 /**
  * A wrapper around a database transaction. Transactions are not thread-safe.
  */
@@ -17,7 +19,7 @@ public class Transaction {
 	private final Object txn;
 	private final boolean readOnly;
 
-	private List<Event> events = null;
+	private List<CommitAction> actions = null;
 	private boolean committed = false;
 
 	public Transaction(Object txn, boolean readOnly) {
@@ -42,19 +44,27 @@ public class Transaction {
 
 	/**
 	 * Attaches an event to be broadcast when the transaction has been
-	 * committed.
+	 * committed. The event will be broadcast on the {@link EventExecutor}.
 	 */
 	public void attach(Event e) {
-		if (events == null) events = new ArrayList<>();
-		events.add(e);
+		if (actions == null) actions = new ArrayList<>();
+		actions.add(new EventAction(e));
 	}
 
 	/**
-	 * Returns any events attached to the transaction.
+	 * Attaches a task to be executed when the transaction has been
+	 * committed. The task will be run on the {@link EventExecutor}.
 	 */
-	public List<Event> getEvents() {
-		if (events == null) return Collections.emptyList();
-		return events;
+	public void attach(Runnable r) {
+		if (actions == null) actions = new ArrayList<>();
+		actions.add(new TaskAction(r));
+	}
+
+	/**
+	 * Returns any actions attached to the transaction.
+	 */
+	public List<CommitAction> getActions() {
+		return actions == null ? emptyList() : actions;
 	}
 
 	/**

bramble-api/src/main/java/org/briarproject/bramble/api/event/EventBus.java

@@ -16,7 +16,8 @@ public interface EventBus {
 	void removeListener(EventListener l);
 
 	/**
-	 * Notifies all listeners of an event.
+	 * Asynchronously notifies all listeners of an event. Listeners are
+	 * notified on the {@link EventExecutor}.
 	 */
 	void broadcast(Event e);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/event/EventExecutor.java

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api.event;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+/**
+ * Annotation for injecting the executor for broadcasting events and running
+ * tasks that need to run in a defined order with respect to events. Also used
+ * for annotating methods that should run on the event executor.
+ * <p>
+ * The contract of this executor is that tasks are run in the order they're
+ * submitted, tasks are not run concurrently, and submitting a task will never
+ * block. Tasks must not block. Tasks submitted during shutdown are discarded.
+ */
+@Qualifier
+@Target({FIELD, METHOD, PARAMETER})
+@Retention(RUNTIME)
+public @interface EventExecutor {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/event/EventListener.java

@@ -12,5 +12,6 @@ public interface EventListener {
 	 * Called when an event is broadcast. Implementations of this method must
 	 * not block.
 	 */
+	@EventExecutor
 	void eventOccurred(Event e);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/identity/AuthorFactory.java

@@ -18,14 +18,7 @@ public interface AuthorFactory {
 
 	/**
 	 * Creates a local author with the current format version and the given
-	 * name and keys.
+	 * name.
 	 */
-	LocalAuthor createLocalAuthor(String name, byte[] publicKey,
-			byte[] privateKey);
-
-	/**
-	 * Creates a local author with the given format version, name and keys.
-	 */
-	LocalAuthor createLocalAuthor(int formatVersion, String name,
-			byte[] publicKey, byte[] privateKey);
+	LocalAuthor createLocalAuthor(String name);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/identity/Identity.java

@@ -0,0 +1,96 @@
+package org.briarproject.bramble.api.identity;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.Arrays;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.bramble.api.crypto.CryptoConstants.MAX_AGREEMENT_PUBLIC_KEY_BYTES;
+
+@Immutable
+@NotNullByDefault
+public class Identity {
+
+	private final LocalAuthor localAuthor;
+	@Nullable
+	private final byte[] handshakePublicKey, handshakePrivateKey;
+	private final long created;
+
+	public Identity(LocalAuthor localAuthor,
+			@Nullable byte[] handshakePublicKey,
+			@Nullable byte[] handshakePrivateKey, long created) {
+		if (handshakePublicKey != null) {
+			int keyLength = handshakePublicKey.length;
+			if (keyLength == 0 || keyLength > MAX_AGREEMENT_PUBLIC_KEY_BYTES)
+				throw new IllegalArgumentException();
+		}
+		this.localAuthor = localAuthor;
+		this.handshakePublicKey = handshakePublicKey;
+		this.handshakePrivateKey = handshakePrivateKey;
+		this.created = created;
+	}
+
+	/**
+	 * Returns the ID of the user's pseudonym.
+	 */
+	public AuthorId getId() {
+		return localAuthor.getId();
+	}
+
+	/**
+	 * Returns the user's pseudonym.
+	 */
+	public LocalAuthor getLocalAuthor() {
+		return localAuthor;
+	}
+
+	/**
+	 * Returns true if the identity has a handshake key pair.
+	 */
+	public boolean hasHandshakeKeyPair() {
+		return handshakePublicKey != null && handshakePrivateKey != null;
+	}
+
+	/**
+	 * Returns the public key used for handshaking, or null if no key exists.
+	 */
+	@Nullable
+	public byte[] getHandshakePublicKey() {
+		return handshakePublicKey;
+	}
+
+	/**
+	 * Returns the private key used for handshaking, or null if no key exists.
+	 */
+	@Nullable
+	public byte[] getHandshakePrivateKey() {
+		return handshakePrivateKey;
+	}
+
+	/**
+	 * Returns the time the identity was created, in milliseconds since the
+	 * Unix epoch.
+	 */
+	public long getTimeCreated() {
+		return created;
+	}
+
+	@Override
+	public int hashCode() {
+		return localAuthor.getId().hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (o instanceof Identity) {
+			Identity i = (Identity) o;
+			return created == i.created &&
+					localAuthor.equals(i.localAuthor) &&
+					Arrays.equals(handshakePublicKey, i.handshakePublicKey) &&
+					Arrays.equals(handshakePrivateKey, i.handshakePrivateKey);
+		}
+		return false;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/identity/IdentityManager.java

@@ -1,30 +1,29 @@
 package org.briarproject.bramble.api.identity;
 
 import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 @NotNullByDefault
 public interface IdentityManager {
 
 	/**
-	 * Creates a local identity with the given name.
+	 * Creates an identity with the given name. The identity includes a
+	 * handshake key pair.
 	 */
 	@CryptoExecutor
-	LocalAuthor createLocalAuthor(String name);
+	Identity createIdentity(String name);
 
 	/**
-	 * Registers the given local identity with the manager. The identity is
-	 * not stored until {@link #storeLocalAuthor()} is called.
+	 * Registers the given identity with the manager. This method should be
+	 * called before {@link LifecycleManager#startServices(SecretKey)}. The
+	 * identity is stored when {@link LifecycleManager#startServices(SecretKey)}
+	 * is called. The identity must include a handshake key pair.
 	 */
-	void registerLocalAuthor(LocalAuthor a);
-
-	/**
-	 * Stores the local identity registered with
-	 * {@link #registerLocalAuthor(LocalAuthor)}, if any.
-	 */
-	void storeLocalAuthor() throws DbException;
+	void registerIdentity(Identity i);
 
 	/**
 	 * Returns the cached local identity or loads it from the database.
@@ -33,7 +32,18 @@ public interface IdentityManager {
 
 	/**
 	 * Returns the cached local identity or loads it from the database.
+	 * <p/>
+	 * Read-only.
 	 */
 	LocalAuthor getLocalAuthor(Transaction txn) throws DbException;
 
+	/**
+	 * Returns the cached handshake keys or loads them from the database.
+	 * <p/>
+	 * Read-only.
+	 *
+	 * @return A two-element array containing the public key in the first
+	 * element and the private key in the second
+	 */
+	byte[][] getHandshakeKeys(Transaction txn) throws DbException;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/identity/LocalAuthor.java

@@ -12,13 +12,11 @@ import javax.annotation.concurrent.Immutable;
 public class LocalAuthor extends Author {
 
 	private final byte[] privateKey;
-	private final long created;
 
 	public LocalAuthor(AuthorId id, int formatVersion, String name,
-			byte[] publicKey, byte[] privateKey, long created) {
+			byte[] publicKey, byte[] privateKey) {
 		super(id, formatVersion, name, publicKey);
 		this.privateKey = privateKey;
-		this.created = created;
 	}
 
 	/**
@@ -27,12 +25,4 @@ public class LocalAuthor extends Author {
 	public byte[] getPrivateKey() {
 		return privateKey;
 	}
-
-	/**
-	 * Returns the time the pseudonym was created, in milliseconds since the
-	 * Unix epoch.
-	 */
-	public long getTimeCreated() {
-		return created;
-	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/identity/event/IdentityAddedEvent.java

@@ -7,15 +7,15 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import javax.annotation.concurrent.Immutable;
 
 /**
- * An event that is broadcast when a local pseudonym is added.
+ * An event that is broadcast when an identity is added.
  */
 @Immutable
 @NotNullByDefault
-public class LocalAuthorAddedEvent extends Event {
+public class IdentityAddedEvent extends Event {
 
 	private final AuthorId authorId;
 
-	public LocalAuthorAddedEvent(AuthorId authorId) {
+	public IdentityAddedEvent(AuthorId authorId) {
 		this.authorId = authorId;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/identity/event/IdentityRemovedEvent.java

@@ -7,15 +7,15 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import javax.annotation.concurrent.Immutable;
 
 /**
- * An event that is broadcast when a local pseudonym is removed.
+ * An event that is broadcast when an identity is removed.
  */
 @Immutable
 @NotNullByDefault
-public class LocalAuthorRemovedEvent extends Event {
+public class IdentityRemovedEvent extends Event {
 
 	private final AuthorId authorId;
 
-	public LocalAuthorRemovedEvent(AuthorId authorId) {
+	public IdentityRemovedEvent(AuthorId authorId) {
 		this.authorId = authorId;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/keyagreement/KeyAgreementConstants.java

@@ -40,8 +40,8 @@ public interface KeyAgreementConstants {
 			"org.briarproject.bramble.keyagreement/SHARED_SECRET";
 
 	/**
-	 * Label for deriving the master secret.
+	 * Label for deriving the master key.
 	 */
-	String MASTER_SECRET_LABEL =
+	String MASTER_KEY_LABEL =
 			"org.briarproject.bramble.keyagreement/MASTER_SECRET";
 }

bramble-api/src/main/java/org/briarproject/bramble/api/keyagreement/UnsupportedVersionException.java

@@ -1,20 +0,0 @@
-package org.briarproject.bramble.api.keyagreement;
-
-import java.io.IOException;
-
-/**
- * Thrown when a QR code that has been scanned uses a protocol version that is
- * not supported.
- */
-public class UnsupportedVersionException extends IOException {
-
-	private final boolean tooOld;
-
-	public UnsupportedVersionException(boolean tooOld) {
-		this.tooOld = tooOld;
-	}
-
-	public boolean isTooOld() {
-		return tooOld;
-	}
-}

bramble-api/src/main/java/org/briarproject/bramble/api/lifecycle/LifecycleManager.java

@@ -2,16 +2,16 @@ package org.briarproject.bramble.api.lifecycle;
 
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.sync.Client;
 
 import java.util.concurrent.ExecutorService;
 
 /**
- * Manages the lifecycle of the app, starting {@link Client Clients}, starting
- * and stopping {@link Service Services}, shutting down
- * {@link ExecutorService ExecutorServices}, and opening and closing the
- * {@link DatabaseComponent}.
+ * Manages the lifecycle of the app: opening and closing the
+ * {@link DatabaseComponent} starting and stopping {@link Service Services},
+ * and shutting down {@link ExecutorService ExecutorServices}.
  */
 @NotNullByDefault
 public interface LifecycleManager {
@@ -42,18 +42,19 @@ public interface LifecycleManager {
 		}
 	}
 
+	/**
+	 * Registers a hook to be called after the database is opened and before
+	 * {@link Service services} are started. This method should be called
+	 * before {@link #startServices(SecretKey)}.
+	 */
+	void registerOpenDatabaseHook(OpenDatabaseHook hook);
+
 	/**
 	 * Registers a {@link Service} to be started and stopped. This method
 	 * should be called before {@link #startServices(SecretKey)}.
 	 */
 	void registerService(Service s);
 
-	/**
-	 * Registers a {@link Client} to be started. This method should be called
-	 * before {@link #startServices(SecretKey)}.
-	 */
-	void registerClient(Client c);
-
 	/**
 	 * Registers an {@link ExecutorService} to be shut down. This method
 	 * should be called before {@link #startServices(SecretKey)}.
@@ -62,7 +63,7 @@ public interface LifecycleManager {
 
 	/**
 	 * Opens the {@link DatabaseComponent} using the given key and starts any
-	 * registered {@link Client Clients} and {@link Service Services}.
+	 * registered {@link Service Services}.
 	 */
 	StartResult startServices(SecretKey dbKey);
 
@@ -80,8 +81,7 @@ public interface LifecycleManager {
 
 	/**
 	 * Waits for the {@link DatabaseComponent} to be opened and all registered
-	 * {@link Client Clients} and {@link Service Services} to start before
-	 * returning.
+	 * {@link Service Services} to start before returning.
 	 */
 	void waitForStartup() throws InterruptedException;
 
@@ -97,4 +97,13 @@ public interface LifecycleManager {
 	 */
 	LifecycleState getLifecycleState();
 
+	interface OpenDatabaseHook {
+		/**
+		 * Called when the database is being opened, before
+		 * {@link #waitForDatabase()} returns.
+		 *
+		 * @param txn A read-write transaction
+		 */
+		void onDatabaseOpened(Transaction txn) throws DbException;
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/TorConstants.java

@@ -16,6 +16,7 @@ public interface TorConstants {
 	String PREF_TOR_NETWORK = "network2";
 	String PREF_TOR_PORT = "port";
 	String PREF_TOR_MOBILE = "useMobileData";
+	String PREF_TOR_ONLY_WHEN_CHARGING = "onlyWhenCharging";
 
 	int PREF_TOR_NETWORK_AUTOMATIC = 0;
 	int PREF_TOR_NETWORK_WITHOUT_BRIDGES = 1;

bramble-api/src/main/java/org/briarproject/bramble/api/sync/Client.java

@@ -1,14 +0,0 @@
-package org.briarproject.bramble.api.sync;
-
-import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.db.Transaction;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-@NotNullByDefault
-public interface Client {
-
-	/**
-	 * Called at startup to create any local state needed by the client.
-	 */
-	void createLocalState(Transaction txn) throws DbException;
-}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/validation/IncomingMessageHook.java

@@ -11,7 +11,8 @@ public interface IncomingMessageHook {
 	/**
 	 * Called once for each incoming message that passes validation.
 	 *
-	 * @return whether or not this message should be shared
+	 * @param txn A read-write transaction
+	 * @return Whether or not this message should be shared
 	 * @throws DbException Should only be used for real database errors.
 	 * If this is thrown, delivery will be attempted again at next startup,
 	 * whereas if an InvalidMessageException is thrown,

bramble-api/src/main/java/org/briarproject/bramble/api/transport/AbstractTransportKeys.java

@@ -0,0 +1,57 @@
+package org.briarproject.bramble.api.transport;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * Abstract superclass for {@link TransportKeys} and {@link HandshakeKeys}.
+ */
+@Immutable
+@NotNullByDefault
+public abstract class AbstractTransportKeys {
+
+	private final TransportId transportId;
+	private final IncomingKeys inPrev, inCurr, inNext;
+	private final OutgoingKeys outCurr;
+
+	AbstractTransportKeys(TransportId transportId, IncomingKeys inPrev,
+			IncomingKeys inCurr, IncomingKeys inNext, OutgoingKeys outCurr) {
+		if (inPrev.getTimePeriod() != outCurr.getTimePeriod() - 1)
+			throw new IllegalArgumentException();
+		if (inCurr.getTimePeriod() != outCurr.getTimePeriod())
+			throw new IllegalArgumentException();
+		if (inNext.getTimePeriod() != outCurr.getTimePeriod() + 1)
+			throw new IllegalArgumentException();
+		this.transportId = transportId;
+		this.inPrev = inPrev;
+		this.inCurr = inCurr;
+		this.inNext = inNext;
+		this.outCurr = outCurr;
+	}
+
+	public TransportId getTransportId() {
+		return transportId;
+	}
+
+	public IncomingKeys getPreviousIncomingKeys() {
+		return inPrev;
+	}
+
+	public IncomingKeys getCurrentIncomingKeys() {
+		return inCurr;
+	}
+
+	public IncomingKeys getNextIncomingKeys() {
+		return inNext;
+	}
+
+	public OutgoingKeys getCurrentOutgoingKeys() {
+		return outCurr;
+	}
+
+	public long getTimePeriod() {
+		return outCurr.getTimePeriod();
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/transport/HandshakeKeySet.java

@@ -0,0 +1,70 @@
+package org.briarproject.bramble.api.transport;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * A set of keys for handshaking with a given contact or pending contact over a
+ * given transport. Unlike a {@link TransportKeySet} these keys do not provide
+ * forward secrecy.
+ */
+@Immutable
+@NotNullByDefault
+public class HandshakeKeySet {
+
+	private final HandshakeKeySetId keySetId;
+	@Nullable
+	private final ContactId contactId;
+	@Nullable
+	private final PendingContactId pendingContactId;
+	private final HandshakeKeys keys;
+
+	public HandshakeKeySet(HandshakeKeySetId keySetId, ContactId contactId,
+			HandshakeKeys keys) {
+		this.keySetId = keySetId;
+		this.contactId = contactId;
+		this.keys = keys;
+		pendingContactId = null;
+	}
+
+	public HandshakeKeySet(HandshakeKeySetId keySetId,
+			PendingContactId pendingContactId, HandshakeKeys keys) {
+		this.keySetId = keySetId;
+		this.pendingContactId = pendingContactId;
+		this.keys = keys;
+		contactId = null;
+	}
+
+	public HandshakeKeySetId getKeySetId() {
+		return keySetId;
+	}
+
+	@Nullable
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	@Nullable
+	public PendingContactId getPendingContactId() {
+		return pendingContactId;
+	}
+
+	public HandshakeKeys getKeys() {
+		return keys;
+	}
+
+	@Override
+	public int hashCode() {
+		return keySetId.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof HandshakeKeySet &&
+				keySetId.equals(((HandshakeKeySet) o).keySetId);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/transport/HandshakeKeySetId.java

@@ -0,0 +1,36 @@
+package org.briarproject.bramble.api.transport;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * Type-safe wrapper for an integer that uniquely identifies a
+ * {@link HandshakeKeySet set of handshake keys} within the scope of the local
+ * device.
+ */
+@Immutable
+@NotNullByDefault
+public class HandshakeKeySetId {
+
+	private final int id;
+
+	public HandshakeKeySetId(int id) {
+		this.id = id;
+	}
+
+	public int getInt() {
+		return id;
+	}
+
+	@Override
+	public int hashCode() {
+		return id;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof HandshakeKeySetId &&
+				id == ((HandshakeKeySetId) o).id;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/transport/HandshakeKeys.java

@@ -0,0 +1,36 @@
+package org.briarproject.bramble.api.transport;
+
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * Keys for handshaking with a given contact or pending contact over a given
+ * transport. Unlike {@link TransportKeys} these keys do not provide forward
+ * secrecy.
+ */
+@Immutable
+@NotNullByDefault
+public class HandshakeKeys extends AbstractTransportKeys {
+
+	private final SecretKey rootKey;
+	private final boolean alice;
+
+	public HandshakeKeys(TransportId transportId, IncomingKeys inPrev,
+			IncomingKeys inCurr, IncomingKeys inNext, OutgoingKeys outCurr,
+			SecretKey rootKey, boolean alice) {
+		super(transportId, inPrev, inCurr, inNext, outCurr);
+		this.rootKey = rootKey;
+		this.alice = alice;
+	}
+
+	public SecretKey getRootKey() {
+		return rootKey;
+	}
+
+	public boolean isAlice() {
+		return alice;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/transport/IncomingKeys.java

@@ -1,30 +1,35 @@
 package org.briarproject.bramble.api.transport;
 
 import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
 
 import static org.briarproject.bramble.api.transport.TransportConstants.REORDERING_WINDOW_SIZE;
 
 /**
  * Contains transport keys for receiving streams from a given contact over a
- * given transport in a given rotation period.
+ * given transport in a given time period.
  */
+@Immutable
+@NotNullByDefault
 public class IncomingKeys {
 
 	private final SecretKey tagKey, headerKey;
-	private final long rotationPeriod, windowBase;
+	private final long timePeriod, windowBase;
 	private final byte[] windowBitmap;
 
 	public IncomingKeys(SecretKey tagKey, SecretKey headerKey,
-			long rotationPeriod) {
-		this(tagKey, headerKey, rotationPeriod, 0,
+			long timePeriod) {
+		this(tagKey, headerKey, timePeriod, 0,
 				new byte[REORDERING_WINDOW_SIZE / 8]);
 	}
 
 	public IncomingKeys(SecretKey tagKey, SecretKey headerKey,
-			long rotationPeriod, long windowBase, byte[] windowBitmap) {
+			long timePeriod, long windowBase, byte[] windowBitmap) {
 		this.tagKey = tagKey;
 		this.headerKey = headerKey;
-		this.rotationPeriod = rotationPeriod;
+		this.timePeriod = timePeriod;
 		this.windowBase = windowBase;
 		this.windowBitmap = windowBitmap;
 	}
@@ -37,8 +42,8 @@ public class IncomingKeys {
 		return headerKey;
 	}
 
-	public long getRotationPeriod() {
-		return rotationPeriod;
+	public long getTimePeriod() {
+		return timePeriod;
 	}
 
 	public long getWindowBase() {

bramble-api/src/main/java/org/briarproject/bramble/api/transport/KeyManager.java

@@ -27,14 +27,14 @@ public interface KeyManager {
 	 * @param alice true if the local party is Alice
 	 * @param active whether the derived keys can be used for outgoing streams
 	 */
-	Map<TransportId, KeySetId> addContact(Transaction txn, ContactId c,
-			SecretKey master, long timestamp, boolean alice, boolean active)
+	Map<TransportId, TransportKeySetId> addContact(Transaction txn, ContactId c,
+			SecretKey rootKey, long timestamp, boolean alice, boolean active)
 			throws DbException;
 
 	/**
 	 * Marks the given transport keys as usable for outgoing streams.
 	 */
-	void activateKeys(Transaction txn, Map<TransportId, KeySetId> keys)
+	void activateKeys(Transaction txn, Map<TransportId, TransportKeySetId> keys)
 			throws DbException;
 
 	/**

bramble-api/src/main/java/org/briarproject/bramble/api/transport/KeySet.java

@@ -1,47 +0,0 @@
-package org.briarproject.bramble.api.transport;
-
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import javax.annotation.concurrent.Immutable;
-
-/**
- * A set of transport keys for communicating with a contact.
- */
-@Immutable
-@NotNullByDefault
-public class KeySet {
-
-	private final KeySetId keySetId;
-	private final ContactId contactId;
-	private final TransportKeys transportKeys;
-
-	public KeySet(KeySetId keySetId, ContactId contactId,
-			TransportKeys transportKeys) {
-		this.keySetId = keySetId;
-		this.contactId = contactId;
-		this.transportKeys = transportKeys;
-	}
-
-	public KeySetId getKeySetId() {
-		return keySetId;
-	}
-
-	public ContactId getContactId() {
-		return contactId;
-	}
-
-	public TransportKeys getTransportKeys() {
-		return transportKeys;
-	}
-
-	@Override
-	public int hashCode() {
-		return keySetId.hashCode();
-	}
-
-	@Override
-	public boolean equals(Object o) {
-		return o instanceof KeySet && keySetId.equals(((KeySet) o).keySetId);
-	}
-}

bramble-api/src/main/java/org/briarproject/bramble/api/transport/OutgoingKeys.java

@@ -1,27 +1,32 @@
 package org.briarproject.bramble.api.transport;
 
 import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
 
 /**
  * Contains transport keys for sending streams to a given contact over a given
- * transport in a given rotation period.
+ * transport in a given time period.
  */
+@Immutable
+@NotNullByDefault
 public class OutgoingKeys {
 
 	private final SecretKey tagKey, headerKey;
-	private final long rotationPeriod, streamCounter;
+	private final long timePeriod, streamCounter;
 	private final boolean active;
 
 	public OutgoingKeys(SecretKey tagKey, SecretKey headerKey,
-			long rotationPeriod, boolean active) {
-		this(tagKey, headerKey, rotationPeriod, 0, active);
+			long timePeriod, boolean active) {
+		this(tagKey, headerKey, timePeriod, 0, active);
 	}
 
 	public OutgoingKeys(SecretKey tagKey, SecretKey headerKey,
-			long rotationPeriod, long streamCounter, boolean active) {
+			long timePeriod, long streamCounter, boolean active) {
 		this.tagKey = tagKey;
 		this.headerKey = headerKey;
-		this.rotationPeriod = rotationPeriod;
+		this.timePeriod = timePeriod;
 		this.streamCounter = streamCounter;
 		this.active = active;
 	}
@@ -34,8 +39,8 @@ public class OutgoingKeys {
 		return headerKey;
 	}
 
-	public long getRotationPeriod() {
-		return rotationPeriod;
+	public long getTimePeriod() {
+		return timePeriod;
 	}
 
 	public long getStreamCounter() {

bramble-api/src/main/java/org/briarproject/bramble/api/transport/StreamContext.java

@@ -2,8 +2,13 @@ package org.briarproject.bramble.api.transport;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
 public class StreamContext {
 
 	private final ContactId contactId;

bramble-api/src/main/java/org/briarproject/bramble/api/transport/TransportConstants.java

@@ -82,30 +82,58 @@ public interface TransportConstants {
 	int REORDERING_WINDOW_SIZE = 32;
 
 	/**
-	 * Label for deriving Alice's initial tag key from the master secret.
+	 * Label for deriving Alice's initial tag key from the root key in
+	 * rotation mode.
 	 */
 	String ALICE_TAG_LABEL = "org.briarproject.bramble.transport/ALICE_TAG_KEY";
 
 	/**
-	 * Label for deriving Bob's initial tag key from the master secret.
+	 * Label for deriving Bob's initial tag key from the root key in rotation
+	 * mode.
 	 */
 	String BOB_TAG_LABEL = "org.briarproject.bramble.transport/BOB_TAG_KEY";
 
 	/**
-	 * Label for deriving Alice's initial header key from the master secret.
+	 * Label for deriving Alice's initial header key from the root key in
+	 * rotation mode.
 	 */
 	String ALICE_HEADER_LABEL =
 			"org.briarproject.bramble.transport/ALICE_HEADER_KEY";
 
 	/**
-	 * Label for deriving Bob's initial header key from the master secret.
+	 * Label for deriving Bob's initial header key from the root key in
+	 * rotation mode.
 	 */
 	String BOB_HEADER_LABEL =
 			"org.briarproject.bramble.transport/BOB_HEADER_KEY";
 
 	/**
-	 * Label for deriving the next period's key in key rotation.
+	 * Label for deriving the next period's key in rotation mode.
 	 */
 	String ROTATE_LABEL = "org.briarproject.bramble.transport/ROTATE";
 
+	/**
+	 * Label for deriving Alice's tag key from the root key in handshake mode.
+	 */
+	String ALICE_HANDSHAKE_TAG_LABEL =
+			"org.briarproject.bramble.transport/ALICE_HANDSHAKE_TAG_KEY";
+
+	/**
+	 * Label for deriving Bob's tag key from the root key in handshake mode.
+	 */
+	String BOB_HANDSHAKE_TAG_LABEL =
+			"org.briarproject.bramble.transport/BOB_HANDSHAKE_TAG_KEY";
+
+	/**
+	 * Label for deriving Alice's header key from the root key in handshake
+	 * mode.
+	 */
+	String ALICE_HANDSHAKE_HEADER_LABEL =
+			"org.briarproject.bramble.transport/ALICE_HANDSHAKE_HEADER_KEY";
+
+	/**
+	 * Label for deriving Bob's header key from the root key in handshake mode.
+	 */
+	String BOB_HANDSHAKE_HEADER_LABEL =
+			"org.briarproject.bramble.transport/BOB_HANDSHAKE_HEADER_KEY";
 }

bramble-api/src/main/java/org/briarproject/bramble/api/transport/TransportKeySet.java

@@ -0,0 +1,49 @@
+package org.briarproject.bramble.api.transport;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * A set of keys for communicating with a given contact over a given transport.
+ * Unlike a {@link HandshakeKeySet} these keys provide forward secrecy.
+ */
+@Immutable
+@NotNullByDefault
+public class TransportKeySet {
+
+	private final TransportKeySetId keySetId;
+	private final ContactId contactId;
+	private final TransportKeys keys;
+
+	public TransportKeySet(TransportKeySetId keySetId, ContactId contactId,
+			TransportKeys keys) {
+		this.keySetId = keySetId;
+		this.contactId = contactId;
+		this.keys = keys;
+	}
+
+	public TransportKeySetId getKeySetId() {
+		return keySetId;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public TransportKeys getKeys() {
+		return keys;
+	}
+
+	@Override
+	public int hashCode() {
+		return keySetId.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof TransportKeySet &&
+				keySetId.equals(((TransportKeySet) o).keySetId);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/transport/TransportKeySetId.java

@@ -5,18 +5,19 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import javax.annotation.concurrent.Immutable;
 
 /**
- * Type-safe wrapper for an integer that uniquely identifies a set of transport
- * keys within the scope of the local device.
+ * Type-safe wrapper for an integer that uniquely identifies a
+ * {@link TransportKeySet set of transport keys} within the scope of the local
+ * device.
  * <p/>
  * Key sets created on a given device must have increasing identifiers.
  */
 @Immutable
 @NotNullByDefault
-public class KeySetId {
+public class TransportKeySetId {
 
 	private final int id;
 
-	public KeySetId(int id) {
+	public TransportKeySetId(int id) {
 		this.id = id;
 	}
 
@@ -31,6 +32,7 @@ public class KeySetId {
 
 	@Override
 	public boolean equals(Object o) {
-		return o instanceof KeySetId && id == ((KeySetId) o).id;
+		return o instanceof TransportKeySetId &&
+				id == ((TransportKeySetId) o).id;
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/transport/TransportKeys.java

@@ -1,52 +1,20 @@
 package org.briarproject.bramble.api.transport;
 
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 
-/**
- * Keys for communicating with a given contact over a given transport.
- */
-public class TransportKeys {
+import javax.annotation.concurrent.Immutable;
 
-	private final TransportId transportId;
-	private final IncomingKeys inPrev, inCurr, inNext;
-	private final OutgoingKeys outCurr;
+/**
+ * Keys for communicating with a given contact over a given transport. Unlike
+ * {@link HandshakeKeys} these keys provide forward secrecy.
+ */
+@Immutable
+@NotNullByDefault
+public class TransportKeys extends AbstractTransportKeys {
 
 	public TransportKeys(TransportId transportId, IncomingKeys inPrev,
 			IncomingKeys inCurr, IncomingKeys inNext, OutgoingKeys outCurr) {
-		if (inPrev.getRotationPeriod() != inCurr.getRotationPeriod() - 1)
-			throw new IllegalArgumentException();
-		if (inNext.getRotationPeriod() != inCurr.getRotationPeriod() + 1)
-			throw new IllegalArgumentException();
-		if (outCurr.getRotationPeriod() != inCurr.getRotationPeriod())
-			throw new IllegalArgumentException();
-		this.transportId = transportId;
-		this.inPrev = inPrev;
-		this.inCurr = inCurr;
-		this.inNext = inNext;
-		this.outCurr = outCurr;
-	}
-
-	public TransportId getTransportId() {
-		return transportId;
-	}
-
-	public IncomingKeys getPreviousIncomingKeys() {
-		return inPrev;
-	}
-
-	public IncomingKeys getCurrentIncomingKeys() {
-		return inCurr;
-	}
-
-	public IncomingKeys getNextIncomingKeys() {
-		return inNext;
-	}
-
-	public OutgoingKeys getCurrentOutgoingKeys() {
-		return outCurr;
-	}
-
-	public long getRotationPeriod() {
-		return outCurr.getRotationPeriod();
+		super(transportId, inPrev, inCurr, inNext, outCurr);
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/versioning/ClientVersioningManager.java

@@ -38,8 +38,22 @@ public interface ClientVersioningManager {
 	Visibility getClientVisibility(Transaction txn, ContactId contactId,
 			ClientId clientId, int majorVersion) throws DbException;
 
-	interface ClientVersioningHook {
+	/**
+	 * Returns the minor version of the given client that is supported by the
+	 * given contact, or -1 if the contact does not support the client.
+	 */
+	int getClientMinorVersion(Transaction txn, ContactId contactId,
+			ClientId clientId, int majorVersion) throws DbException;
 
+	interface ClientVersioningHook {
+		/**
+		 * Called when the visibility of a client with respect to a contact is
+		 * changing.
+		 *
+		 * @param txn A read-write transaction
+		 * @param c The contact affected by the visibility change
+		 * @param v The new visibility of the client
+		 */
 		void onClientVisibilityChanging(Transaction txn, Contact c,
 				Visibility v) throws DbException;
 	}

bramble-api/src/main/java/org/briarproject/bramble/util/Base32.java

@@ -0,0 +1,75 @@
+package org.briarproject.bramble.util;
+
+import java.io.ByteArrayOutputStream;
+
+public class Base32 {
+
+	private static final char[] DIGITS = {
+			'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
+			'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
+			'Y', 'Z', '2', '3', '4', '5', '6', '7'
+	};
+
+	public static String encode(byte[] b) {
+		StringBuilder s = new StringBuilder();
+		int byteIndex = 0, currentCode = 0x00;
+		int byteMask = 0x80, codeMask = 0x10;
+		while (byteIndex < b.length) {
+			if ((b[byteIndex] & byteMask) != 0) currentCode |= codeMask;
+			// After every 8 bits, move on to the next byte
+			if (byteMask == 0x01) {
+				byteMask = 0x80;
+				byteIndex++;
+			} else {
+				byteMask >>>= 1;
+			}
+			// After every 5 bits, move on to the next digit
+			if (codeMask == 0x01) {
+				s.append(DIGITS[currentCode]);
+				codeMask = 0x10;
+				currentCode = 0x00;
+			} else {
+				codeMask >>>= 1;
+			}
+		}
+		// If we're part-way through a digit, output it
+		if (codeMask != 0x10) s.append(DIGITS[currentCode]);
+		return s.toString();
+	}
+
+	public static byte[] decode(String s, boolean strict) {
+		ByteArrayOutputStream b = new ByteArrayOutputStream();
+		int digitIndex = 0, digitCount = s.length(), currentByte = 0x00;
+		int byteMask = 0x80, codeMask = 0x10;
+		while (digitIndex < digitCount) {
+			int code = decodeDigit(s.charAt(digitIndex));
+			if ((code & codeMask) != 0) currentByte |= byteMask;
+			// After every 8 bits, move on to the next byte
+			if (byteMask == 0x01) {
+				b.write(currentByte);
+				byteMask = 0x80;
+				currentByte = 0x00;
+			} else {
+				byteMask >>>= 1;
+			}
+			// After every 5 bits, move on to the next digit
+			if (codeMask == 0x01) {
+				codeMask = 0x10;
+				digitIndex++;
+			} else {
+				codeMask >>>= 1;
+			}
+		}
+		// If any extra bits were used for encoding, they should all be zero
+		if (strict && byteMask != 0x80 && currentByte != 0x00)
+			throw new IllegalArgumentException();
+		return b.toByteArray();
+	}
+
+	private static int decodeDigit(char c) {
+		if (c >= 'A' && c <= 'Z') return c - 'A';
+		if (c >= 'a' && c <= 'z') return c - 'a';
+		if (c >= '2' && c <= '7') return c - '2' + 26;
+		throw new IllegalArgumentException("Not a base32 digit: " + c);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/util/ByteUtils.java

@@ -1,7 +1,5 @@
 package org.briarproject.bramble.util;
 
-import org.briarproject.bramble.api.FormatException;
-
 public class ByteUtils {
 
 	/**
@@ -14,26 +12,15 @@ public class ByteUtils {
 	 */
 	public static final long MAX_32_BIT_UNSIGNED = 4294967295L; // 2^32 - 1
 
-	/**
-	 * The number of bytes needed to encode a 16-bit integer.
-	 */
+	/** The number of bytes needed to encode a 16-bit integer. */
 	public static final int INT_16_BYTES = 2;
 
-	/**
-	 * The number of bytes needed to encode a 32-bit integer.
-	 */
+	/** The number of bytes needed to encode a 32-bit integer. */
 	public static final int INT_32_BYTES = 4;
 
-	/**
-	 * The number of bytes needed to encode a 64-bit integer.
-	 */
+	/** The number of bytes needed to encode a 64-bit integer. */
 	public static final int INT_64_BYTES = 8;
 
-	/**
-	 * The maximum number of bytes needed to encode a variable-length integer.
-	 */
-	public static final int MAX_VARINT_BYTES = 9;
-
 	public static void writeUint16(int src, byte[] dest, int offset) {
 		if (src < 0) throw new IllegalArgumentException();
 		if (src > MAX_16_BIT_UNSIGNED) throw new IllegalArgumentException();
@@ -68,42 +55,6 @@ public class ByteUtils {
 		dest[offset + 7] = (byte) (src & 0xFF);
 	}
 
-	/**
-	 * Returns the number of bytes needed to represent 'src' as a
-	 * variable-length integer.
-	 * <p>
-	 * 'src' must not be negative.
-	 */
-	public static int getVarIntBytes(long src) {
-		if (src < 0) throw new IllegalArgumentException();
-		int len = 1;
-		while ((src >>= 7) > 0) len++;
-		return len;
-	}
-
-	/**
-	 * Writes 'src' to 'dest' as a variable-length integer, starting at
-	 * 'offset', and returns the number of bytes written.
-	 * <p>
-	 * `src` must not be negative.
-	 */
-	public static int writeVarInt(long src, byte[] dest, int offset) {
-		if (src < 0) throw new IllegalArgumentException();
-		int len = getVarIntBytes(src);
-		if (dest.length < offset + len) throw new IllegalArgumentException();
-		// Work backwards from the end
-		int end = offset + len - 1;
-		for (int i = end; i >= offset; i--) {
-			// Encode 7 bits
-			dest[i] = (byte) (src & 0x7F);
-			// Raise the continuation flag, except for the last byte
-			if (i < end) dest[i] |= (byte) 0x80;
-			// Shift out the bits that were encoded
-			src >>= 7;
-		}
-		return len;
-	}
-
 	public static int readUint16(byte[] src, int offset) {
 		if (src.length < offset + INT_16_BYTES)
 			throw new IllegalArgumentException();
@@ -132,46 +83,14 @@ public class ByteUtils {
 				| (src[offset + 7] & 0xFFL);
 	}
 
-	/**
-	 * Returns the length in bytes of a variable-length integer encoded in
-	 * 'src' starting at 'offset'.
-	 *
-	 * @throws FormatException if there is not a valid variable-length integer
-	 * at the specified position.
-	 */
-	public static int getVarIntBytes(byte[] src, int offset)
-			throws FormatException {
-		if (src.length < offset) throw new IllegalArgumentException();
-		for (int i = 0; i < MAX_VARINT_BYTES && offset + i < src.length; i++) {
-			// If the continuation flag is lowered, this is the last byte
-			if ((src[offset + i] & 0x80) == 0) return i + 1;
+	public static int readUint(byte[] src, int bits) {
+		if (src.length << 3 < bits) throw new IllegalArgumentException();
+		int dest = 0;
+		for (int i = 0; i < bits; i++) {
+			if ((src[i >> 3] & 128 >> (i & 7)) != 0) dest |= 1 << bits - i - 1;
 		}
-		// We've read 9 bytes or reached the end of the input without finding
-		// the last byte
-		throw new FormatException();
-	}
-
-	/**
-	 * Reads a variable-length integer from 'src' starting at 'offset' and
-	 * returns it.
-	 *
-	 * @throws FormatException if there is not a valid variable-length integer
-	 * at the specified position.
-	 */
-	public static long readVarInt(byte[] src, int offset)
-			throws FormatException {
-		if (src.length < offset) throw new IllegalArgumentException();
-		long dest = 0;
-		for (int i = 0; i < MAX_VARINT_BYTES && offset + i < src.length; i++) {
-			// Decode 7 bits
-			dest |= src[offset + i] & 0x7F;
-			// If the continuation flag is lowered, this is the last byte
-			if ((src[offset + i] & 0x80) == 0) return dest;
-			// Make room for the next 7 bits
-			dest <<= 7;
-		}
-		// We've read 9 bytes or reached the end of the input without finding
-		// the last byte
-		throw new FormatException();
+		if (dest < 0) throw new AssertionError();
+		if (dest >= 1 << bits) throw new AssertionError();
+		return dest;
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/util/StringUtils.java

@@ -153,4 +153,13 @@ public class StringUtils {
 		return new String(c);
 	}
 
+	public static String getRandomBase32String(int length) {
+		char[] c = new char[length];
+		for (int i = 0; i < length; i++) {
+			int character = random.nextInt(32);
+			if (character < 26) c[i] = (char) ('a' + character);
+			else c[i] = (char) ('2' + (character - 26));
+		}
+		return new String(c);
+	}
 }

bramble-api/src/test/java/org/briarproject/bramble/test/TestUtils.java

@@ -1,9 +1,14 @@
 package org.briarproject.bramble.test;
 
 import org.briarproject.bramble.api.UniqueId;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorId;
+import org.briarproject.bramble.api.identity.Identity;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.properties.TransportProperties;
@@ -25,6 +30,8 @@ import java.util.Random;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static java.util.Arrays.asList;
+import static org.briarproject.bramble.api.contact.PendingContactState.WAITING_FOR_CONNECTION;
+import static org.briarproject.bramble.api.crypto.CryptoConstants.MAX_AGREEMENT_PUBLIC_KEY_BYTES;
 import static org.briarproject.bramble.api.identity.Author.FORMAT_VERSION;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_PUBLIC_KEY_LENGTH;
@@ -41,6 +48,7 @@ public class TestUtils {
 			new AtomicInteger((int) (Math.random() * 1000 * 1000));
 	private static final Random random = new Random();
 	private static final long timestamp = System.currentTimeMillis();
+	private static final AtomicInteger nextContactId = new AtomicInteger(1);
 
 	public static File getTestDirectory() {
 		int name = nextTestDir.getAndIncrement();
@@ -93,25 +101,26 @@ public class TestUtils {
 		return new SecretKey(getRandomBytes(SecretKey.LENGTH));
 	}
 
-	public static LocalAuthor getLocalAuthor() {
-		return getLocalAuthor(1 + random.nextInt(MAX_AUTHOR_NAME_LENGTH));
-	}
-
-	public static LocalAuthor getLocalAuthor(int nameLength) {
-		AuthorId id = new AuthorId(getRandomId());
-		String name = getRandomString(nameLength);
-		byte[] publicKey = getRandomBytes(MAX_PUBLIC_KEY_LENGTH);
-		byte[] privateKey = getRandomBytes(MAX_PUBLIC_KEY_LENGTH);
-		return new LocalAuthor(id, FORMAT_VERSION, name, publicKey, privateKey,
+	public static Identity getIdentity() {
+		LocalAuthor localAuthor = getLocalAuthor();
+		byte[] handshakePub = getRandomBytes(MAX_AGREEMENT_PUBLIC_KEY_BYTES);
+		byte[] handshakePriv = getRandomBytes(MAX_AGREEMENT_PUBLIC_KEY_BYTES);
+		return new Identity(localAuthor, handshakePub, handshakePriv,
 				timestamp);
 	}
 
-	public static Author getAuthor() {
-		return getAuthor(1 + random.nextInt(MAX_AUTHOR_NAME_LENGTH));
+	public static LocalAuthor getLocalAuthor() {
+		AuthorId id = new AuthorId(getRandomId());
+		int nameLength = 1 + random.nextInt(MAX_AUTHOR_NAME_LENGTH);
+		String name = getRandomString(nameLength);
+		byte[] publicKey = getRandomBytes(MAX_PUBLIC_KEY_LENGTH);
+		byte[] privateKey = getRandomBytes(MAX_PUBLIC_KEY_LENGTH);
+		return new LocalAuthor(id, FORMAT_VERSION, name, publicKey, privateKey);
 	}
 
-	public static Author getAuthor(int nameLength) {
+	public static Author getAuthor() {
 		AuthorId id = new AuthorId(getRandomId());
+		int nameLength = 1 + random.nextInt(MAX_AUTHOR_NAME_LENGTH);
 		String name = getRandomString(nameLength);
 		byte[] publicKey = getRandomBytes(MAX_PUBLIC_KEY_LENGTH);
 		return new Author(id, FORMAT_VERSION, name, publicKey);
@@ -140,6 +149,39 @@ public class TestUtils {
 		return new Message(id, groupId, timestamp, body);
 	}
 
+	public static PendingContact getPendingContact() {
+		return getPendingContact(1 + random.nextInt(MAX_AUTHOR_NAME_LENGTH));
+	}
+
+	public static PendingContact getPendingContact(int nameLength) {
+		PendingContactId id = new PendingContactId(getRandomId());
+		byte[] publicKey = getRandomBytes(MAX_PUBLIC_KEY_LENGTH);
+		String alias = getRandomString(nameLength);
+		return new PendingContact(id, publicKey, alias, WAITING_FOR_CONNECTION,
+				timestamp);
+	}
+
+	public static ContactId getContactId() {
+		return new ContactId(nextContactId.getAndIncrement());
+	}
+
+	public static Contact getContact() {
+		return getContact(getAuthor(), new AuthorId(getRandomId()),
+				random.nextBoolean());
+	}
+
+	public static Contact getContact(Author remote, AuthorId local,
+			boolean verified) {
+		return getContact(getContactId(), remote, local, verified);
+	}
+
+	public static Contact getContact(ContactId c, Author remote, AuthorId local,
+			boolean verified) {
+		return new Contact(c, remote, local,
+				getRandomString(MAX_AUTHOR_NAME_LENGTH),
+				getRandomBytes(MAX_PUBLIC_KEY_LENGTH), verified);
+	}
+
 	public static double getMedian(Collection<? extends Number> samples) {
 		int size = samples.size();
 		if (size == 0) throw new IllegalArgumentException();

bramble-api/witness.gradle

@@ -2,7 +2,7 @@ dependencyVerification {
     verify = [
         'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
-        'com.google.dagger:dagger:2.19:dagger-2.19.jar:514b6f1e0727c6572e1d65cb27e4ae668b7aeaeb93a29515182965265b609939',
+        'com.google.dagger:dagger:2.22.1:dagger-2.22.1.jar:329d4340f24c4f5717af016c097e90668bfea2a5376e6aa9964b01cef3fd241a',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
         'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
         'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',

bramble-core/build.gradle

@@ -17,7 +17,7 @@ dependencies {
 	implementation 'org.whispersystems:curve25519-java:0.5.0'
 	implementation 'org.briarproject:jtorctl:0.3'
 
-	annotationProcessor 'com.google.dagger:dagger-compiler:2.19'
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.22.1'
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	testImplementation 'org.hsqldb:hsqldb:2.3.5' // The last version that supports Java 1.6
@@ -26,7 +26,7 @@ dependencies {
 	testImplementation "org.jmock:jmock-junit4:2.8.2"
 	testImplementation "org.jmock:jmock-legacy:2.8.2"
 
-	testAnnotationProcessor 'com.google.dagger:dagger-compiler:2.19'
+	testAnnotationProcessor 'com.google.dagger:dagger-compiler:2.22.1'
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }

bramble-core/src/main/java/org/briarproject/bramble/account/AccountManagerImpl.java

@@ -4,8 +4,8 @@ import org.briarproject.bramble.api.account.AccountManager;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DatabaseConfig;
+import org.briarproject.bramble.api.identity.Identity;
 import org.briarproject.bramble.api.identity.IdentityManager;
-import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.util.IoUtils;
@@ -161,8 +161,8 @@ class AccountManagerImpl implements AccountManager {
 		synchronized (stateChangeLock) {
 			if (hasDatabaseKey())
 				throw new AssertionError("Already have a database key");
-			LocalAuthor localAuthor = identityManager.createLocalAuthor(name);
-			identityManager.registerLocalAuthor(localAuthor);
+			Identity identity = identityManager.createIdentity(name);
+			identityManager.registerIdentity(identity);
 			SecretKey key = crypto.generateSecretKey();
 			if (!encryptAndStoreDatabaseKey(key, password)) return false;
 			databaseKey = key;

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactExchangeTaskImpl.java

@@ -2,10 +2,11 @@ package org.briarproject.bramble.contact;
 
 import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.client.ClientHelper;
-import org.briarproject.bramble.api.contact.ContactExchangeListener;
 import org.briarproject.bramble.api.contact.ContactExchangeTask;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.contact.event.ContactExchangeFailedEvent;
+import org.briarproject.bramble.api.contact.event.ContactExchangeSucceededEvent;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.data.BdfDictionary;
@@ -13,6 +14,7 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.db.ContactExistsException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
@@ -63,6 +65,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	private final ClientHelper clientHelper;
 	private final RecordReaderFactory recordReaderFactory;
 	private final RecordWriterFactory recordWriterFactory;
+	private final EventBus eventBus;
 	private final Clock clock;
 	private final ConnectionManager connectionManager;
 	private final ContactManager contactManager;
@@ -71,18 +74,18 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	private final StreamReaderFactory streamReaderFactory;
 	private final StreamWriterFactory streamWriterFactory;
 
-	private volatile ContactExchangeListener listener;
 	private volatile LocalAuthor localAuthor;
 	private volatile DuplexTransportConnection conn;
 	private volatile TransportId transportId;
-	private volatile SecretKey masterSecret;
+	private volatile SecretKey masterKey;
 	private volatile boolean alice;
 
 	@Inject
 	ContactExchangeTaskImpl(DatabaseComponent db, ClientHelper clientHelper,
 			RecordReaderFactory recordReaderFactory,
-			RecordWriterFactory recordWriterFactory, Clock clock,
-			ConnectionManager connectionManager, ContactManager contactManager,
+			RecordWriterFactory recordWriterFactory, EventBus eventBus,
+			Clock clock, ConnectionManager connectionManager,
+			ContactManager contactManager,
 			TransportPropertyManager transportPropertyManager,
 			CryptoComponent crypto, StreamReaderFactory streamReaderFactory,
 			StreamWriterFactory streamWriterFactory) {
@@ -90,6 +93,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 		this.clientHelper = clientHelper;
 		this.recordReaderFactory = recordReaderFactory;
 		this.recordWriterFactory = recordWriterFactory;
+		this.eventBus = eventBus;
 		this.clock = clock;
 		this.connectionManager = connectionManager;
 		this.contactManager = contactManager;
@@ -100,15 +104,13 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 	}
 
 	@Override
-	public void startExchange(ContactExchangeListener listener,
-			LocalAuthor localAuthor, SecretKey masterSecret,
+	public void startExchange(LocalAuthor localAuthor, SecretKey masterKey,
 			DuplexTransportConnection conn, TransportId transportId,
 			boolean alice) {
-		this.listener = listener;
 		this.localAuthor = localAuthor;
 		this.conn = conn;
 		this.transportId = transportId;
-		this.masterSecret = masterSecret;
+		this.masterKey = masterKey;
 		this.alice = alice;
 		start();
 	}
@@ -123,8 +125,8 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 			out = conn.getWriter().getOutputStream();
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
-			listener.contactExchangeFailed();
 			tryToClose(conn);
+			eventBus.broadcast(new ContactExchangeFailedEvent());
 			return;
 		}
 
@@ -134,15 +136,15 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 			localProperties = transportPropertyManager.getLocalProperties();
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
-			listener.contactExchangeFailed();
+			eventBus.broadcast(new ContactExchangeFailedEvent());
 			tryToClose(conn);
 			return;
 		}
 
 		// Derive the header keys for the transport streams
-		SecretKey aliceHeaderKey = crypto.deriveKey(ALICE_KEY_LABEL,
-				masterSecret, new byte[] {PROTOCOL_VERSION});
-		SecretKey bobHeaderKey = crypto.deriveKey(BOB_KEY_LABEL, masterSecret,
+		SecretKey aliceHeaderKey = crypto.deriveKey(ALICE_KEY_LABEL, masterKey,
+				new byte[] {PROTOCOL_VERSION});
+		SecretKey bobHeaderKey = crypto.deriveKey(BOB_KEY_LABEL, masterKey,
 				new byte[] {PROTOCOL_VERSION});
 
 		// Create the readers
@@ -161,9 +163,9 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 						.createRecordWriter(streamWriter.getOutputStream());
 
 		// Derive the nonces to be signed
-		byte[] aliceNonce = crypto.mac(ALICE_NONCE_LABEL, masterSecret,
+		byte[] aliceNonce = crypto.mac(ALICE_NONCE_LABEL, masterKey,
 				new byte[] {PROTOCOL_VERSION});
-		byte[] bobNonce = crypto.mac(BOB_NONCE_LABEL, masterSecret,
+		byte[] bobNonce = crypto.mac(BOB_NONCE_LABEL, masterKey,
 				new byte[] {PROTOCOL_VERSION});
 		byte[] localNonce = alice ? aliceNonce : bobNonce;
 		byte[] remoteNonce = alice ? bobNonce : aliceNonce;
@@ -196,7 +198,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 			}
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
-			listener.contactExchangeFailed();
+			eventBus.broadcast(new ContactExchangeFailedEvent());
 			tryToClose(conn);
 			return;
 		}
@@ -204,7 +206,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 		// Verify the contact's signature
 		if (!verify(remoteInfo.author, remoteNonce, remoteInfo.signature)) {
 			LOG.warning("Invalid signature");
-			listener.contactExchangeFailed();
+			eventBus.broadcast(new ContactExchangeFailedEvent());
 			tryToClose(conn);
 			return;
 		}
@@ -221,15 +223,17 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 					conn);
 			// Pseudonym exchange succeeded
 			LOG.info("Pseudonym exchange succeeded");
-			listener.contactExchangeSucceeded(remoteInfo.author);
+			eventBus.broadcast(
+					new ContactExchangeSucceededEvent(remoteInfo.author));
 		} catch (ContactExistsException e) {
 			logException(LOG, WARNING, e);
 			tryToClose(conn);
-			listener.duplicateContact(remoteInfo.author);
+			eventBus.broadcast(
+					new ContactExchangeFailedEvent(remoteInfo.author));
 		} catch (DbException e) {
 			logException(LOG, WARNING, e);
 			tryToClose(conn);
-			listener.contactExchangeFailed();
+			eventBus.broadcast(new ContactExchangeFailedEvent());
 		}
 	}
 
@@ -289,7 +293,7 @@ class ContactExchangeTaskImpl extends Thread implements ContactExchangeTask {
 			throws DbException {
 		return db.transactionWithResult(false, txn -> {
 			ContactId contactId = contactManager.addContact(txn, remoteAuthor,
-					localAuthor.getId(), masterSecret, timestamp, alice,
+					localAuthor.getId(), masterKey, timestamp, alice,
 					true, true);
 			transportPropertyManager.addRemoteProperties(txn, contactId,
 					remoteProperties);

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactManagerImpl.java

@@ -1,8 +1,11 @@
 package org.briarproject.bramble.contact;
 
+import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
@@ -16,7 +19,6 @@ import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.transport.KeyManager;
 
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
@@ -25,28 +27,36 @@ import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.BASE32_LINK_BYTES;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.OURSELVES;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.UNKNOWN;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.UNVERIFIED;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.VERIFIED;
+import static org.briarproject.bramble.util.StringUtils.getRandomBase32String;
 import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 @ThreadSafe
 @NotNullByDefault
 class ContactManagerImpl implements ContactManager {
 
+	private static final String REMOTE_CONTACT_LINK =
+			"briar://" + getRandomBase32String(BASE32_LINK_BYTES);
+
 	private final DatabaseComponent db;
 	private final KeyManager keyManager;
 	private final IdentityManager identityManager;
+	private final PendingContactFactory pendingContactFactory;
 	private final List<ContactHook> hooks;
 
 	@Inject
 	ContactManagerImpl(DatabaseComponent db, KeyManager keyManager,
-			IdentityManager identityManager) {
+			IdentityManager identityManager,
+			PendingContactFactory pendingContactFactory) {
 		this.db = db;
 		this.keyManager = keyManager;
 		this.identityManager = identityManager;
+		this.pendingContactFactory = pendingContactFactory;
 		hooks = new CopyOnWriteArrayList<>();
 	}
 
@@ -57,10 +67,10 @@ class ContactManagerImpl implements ContactManager {
 
 	@Override
 	public ContactId addContact(Transaction txn, Author remote, AuthorId local,
-			SecretKey master, long timestamp, boolean alice, boolean verified,
+			SecretKey rootKey, long timestamp, boolean alice, boolean verified,
 			boolean active) throws DbException {
-		ContactId c = db.addContact(txn, remote, local, verified, active);
-		keyManager.addContact(txn, c, master, timestamp, alice, active);
+		ContactId c = db.addContact(txn, remote, local, verified);
+		keyManager.addContact(txn, c, rootKey, timestamp, alice, active);
 		Contact contact = db.getContact(txn, c);
 		for (ContactHook hook : hooks) hook.addingContact(txn, contact);
 		return c;
@@ -68,22 +78,47 @@ class ContactManagerImpl implements ContactManager {
 
 	@Override
 	public ContactId addContact(Transaction txn, Author remote, AuthorId local,
-			boolean verified, boolean active) throws DbException {
-		ContactId c = db.addContact(txn, remote, local, verified, active);
+			boolean verified) throws DbException {
+		ContactId c = db.addContact(txn, remote, local, verified);
 		Contact contact = db.getContact(txn, c);
 		for (ContactHook hook : hooks) hook.addingContact(txn, contact);
 		return c;
 	}
 
 	@Override
-	public ContactId addContact(Author remote, AuthorId local, SecretKey master,
-			long timestamp, boolean alice, boolean verified, boolean active)
-			throws DbException {
+	public ContactId addContact(Author remote, AuthorId local,
+			SecretKey rootKey, long timestamp, boolean alice, boolean verified,
+			boolean active) throws DbException {
 		return db.transactionWithResult(false, txn ->
-				addContact(txn, remote, local, master, timestamp, alice,
+				addContact(txn, remote, local, rootKey, timestamp, alice,
 						verified, active));
 	}
 
+	@Override
+	public String getHandshakeLink() {
+		// TODO replace with real implementation
+		return REMOTE_CONTACT_LINK;
+	}
+
+	@Override
+	public PendingContact addPendingContact(String link, String alias)
+			throws DbException, FormatException {
+		PendingContact p =
+				pendingContactFactory.createPendingContact(link, alias);
+		db.transaction(false, txn -> db.addPendingContact(txn, p));
+		return p;
+	}
+
+	@Override
+	public Collection<PendingContact> getPendingContacts() throws DbException {
+		return db.transactionWithResult(true, db::getPendingContacts);
+	}
+
+	@Override
+	public void removePendingContact(PendingContactId p) throws DbException {
+		db.transaction(false, txn -> db.removePendingContact(txn, p));
+	}
+
 	@Override
 	public Contact getContact(ContactId c) throws DbException {
 		return db.transactionWithResult(true, txn -> db.getContact(txn, c));
@@ -110,12 +145,8 @@ class ContactManagerImpl implements ContactManager {
 	}
 
 	@Override
-	public Collection<Contact> getActiveContacts() throws DbException {
-		Collection<Contact> contacts =
-				db.transactionWithResult(true, db::getContacts);
-		List<Contact> active = new ArrayList<>(contacts.size());
-		for (Contact c : contacts) if (c.isActive()) active.add(c);
-		return active;
+	public Collection<Contact> getContacts() throws DbException {
+		return db.transactionWithResult(true, db::getContacts);
 	}
 
 	@Override
@@ -123,12 +154,6 @@ class ContactManagerImpl implements ContactManager {
 		db.transaction(false, txn -> removeContact(txn, c));
 	}
 
-	@Override
-	public void setContactActive(Transaction txn, ContactId c, boolean active)
-			throws DbException {
-		db.setContactActive(txn, c, active);
-	}
-
 	@Override
 	public void setContactAlias(Transaction txn, ContactId c,
 			@Nullable String alias) throws DbException {

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactModule.java

@@ -28,4 +28,10 @@ public class ContactModule {
 			ContactExchangeTaskImpl contactExchangeTask) {
 		return contactExchangeTask;
 	}
+
+	@Provides
+	PendingContactFactory providePendingContactFactory(
+			PendingContactFactoryImpl pendingContactFactory) {
+		return pendingContactFactory;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/contact/PendingContactFactory.java

@@ -0,0 +1,18 @@
+package org.briarproject.bramble.contact;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.UnsupportedVersionException;
+import org.briarproject.bramble.api.contact.PendingContact;
+
+interface PendingContactFactory {
+
+	/**
+	 * Creates a {@link PendingContact} from the given handshake link and alias.
+	 *
+	 * @throws UnsupportedVersionException If the link uses a format version
+	 * that is not supported
+	 * @throws FormatException If the link is invalid
+	 */
+	PendingContact createPendingContact(String link, String alias)
+			throws FormatException;
+}

bramble-core/src/main/java/org/briarproject/bramble/contact/PendingContactFactoryImpl.java

@@ -0,0 +1,70 @@
+package org.briarproject.bramble.contact;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.UnsupportedVersionException;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.crypto.KeyParser;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.util.Base32;
+
+import java.security.GeneralSecurityException;
+import java.util.regex.Matcher;
+
+import javax.inject.Inject;
+
+import static java.lang.System.arraycopy;
+import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.FORMAT_VERSION;
+import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.ID_LABEL;
+import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.LINK_REGEX;
+import static org.briarproject.bramble.api.contact.HandshakeLinkConstants.RAW_LINK_BYTES;
+import static org.briarproject.bramble.api.contact.PendingContactState.WAITING_FOR_CONNECTION;
+
+class PendingContactFactoryImpl implements PendingContactFactory {
+
+	private final CryptoComponent crypto;
+	private final Clock clock;
+
+	@Inject
+	PendingContactFactoryImpl(CryptoComponent crypto, Clock clock) {
+		this.crypto = crypto;
+		this.clock = clock;
+	}
+
+	@Override
+	public PendingContact createPendingContact(String link, String alias)
+			throws FormatException {
+		PublicKey publicKey = parseHandshakeLink(link);
+		PendingContactId id = getPendingContactId(publicKey);
+		long timestamp = clock.currentTimeMillis();
+		return new PendingContact(id, publicKey.getEncoded(), alias,
+				WAITING_FOR_CONNECTION, timestamp);
+	}
+
+	private PublicKey parseHandshakeLink(String link) throws FormatException {
+		Matcher matcher = LINK_REGEX.matcher(link);
+		if (!matcher.find()) throw new FormatException();
+		// Discard 'briar://' and anything before or after the link
+		link = matcher.group(2);
+		byte[] base32 = Base32.decode(link, false);
+		if (base32.length != RAW_LINK_BYTES) throw new AssertionError();
+		byte version = base32[0];
+		if (version != FORMAT_VERSION)
+			throw new UnsupportedVersionException(version < FORMAT_VERSION);
+		byte[] publicKeyBytes = new byte[base32.length - 1];
+		arraycopy(base32, 1, publicKeyBytes, 0, publicKeyBytes.length);
+		try {
+			KeyParser parser = crypto.getAgreementKeyParser();
+			return parser.parsePublicKey(publicKeyBytes);
+		} catch (GeneralSecurityException e) {
+			throw new FormatException();
+		}
+	}
+
+	private PendingContactId getPendingContactId(PublicKey publicKey) {
+		byte[] hash = crypto.hash(ID_LABEL, publicKey.getEncoded());
+		return new PendingContactId(hash);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/crypto/TransportCryptoImpl.java

@@ -4,18 +4,22 @@ import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.crypto.TransportCrypto;
 import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.transport.HandshakeKeys;
 import org.briarproject.bramble.api.transport.IncomingKeys;
 import org.briarproject.bramble.api.transport.OutgoingKeys;
 import org.briarproject.bramble.api.transport.TransportKeys;
-import org.briarproject.bramble.util.ByteUtils;
-import org.briarproject.bramble.util.StringUtils;
 import org.spongycastle.crypto.Digest;
 import org.spongycastle.crypto.digests.Blake2bDigest;
 
 import javax.inject.Inject;
 
+import static java.lang.System.arraycopy;
+import static org.briarproject.bramble.api.transport.TransportConstants.ALICE_HANDSHAKE_HEADER_LABEL;
+import static org.briarproject.bramble.api.transport.TransportConstants.ALICE_HANDSHAKE_TAG_LABEL;
 import static org.briarproject.bramble.api.transport.TransportConstants.ALICE_HEADER_LABEL;
 import static org.briarproject.bramble.api.transport.TransportConstants.ALICE_TAG_LABEL;
+import static org.briarproject.bramble.api.transport.TransportConstants.BOB_HANDSHAKE_HEADER_LABEL;
+import static org.briarproject.bramble.api.transport.TransportConstants.BOB_HANDSHAKE_TAG_LABEL;
 import static org.briarproject.bramble.api.transport.TransportConstants.BOB_HEADER_LABEL;
 import static org.briarproject.bramble.api.transport.TransportConstants.BOB_TAG_LABEL;
 import static org.briarproject.bramble.api.transport.TransportConstants.ROTATE_LABEL;
@@ -24,6 +28,9 @@ import static org.briarproject.bramble.util.ByteUtils.INT_16_BYTES;
 import static org.briarproject.bramble.util.ByteUtils.INT_64_BYTES;
 import static org.briarproject.bramble.util.ByteUtils.MAX_16_BIT_UNSIGNED;
 import static org.briarproject.bramble.util.ByteUtils.MAX_32_BIT_UNSIGNED;
+import static org.briarproject.bramble.util.ByteUtils.writeUint16;
+import static org.briarproject.bramble.util.ByteUtils.writeUint64;
+import static org.briarproject.bramble.util.StringUtils.toUtf8;
 
 class TransportCryptoImpl implements TransportCrypto {
 
@@ -36,45 +43,44 @@ class TransportCryptoImpl implements TransportCrypto {
 
 	@Override
 	public TransportKeys deriveTransportKeys(TransportId t,
-			SecretKey master, long rotationPeriod, boolean alice,
+			SecretKey rootKey, long timePeriod, boolean weAreAlice,
 			boolean active) {
-		// Keys for the previous period are derived from the master secret
-		SecretKey inTagPrev = deriveTagKey(master, t, !alice);
-		SecretKey inHeaderPrev = deriveHeaderKey(master, t, !alice);
-		SecretKey outTagPrev = deriveTagKey(master, t, alice);
-		SecretKey outHeaderPrev = deriveHeaderKey(master, t, alice);
+		// Keys for the previous period are derived from the root key
+		SecretKey inTagPrev = deriveTagKey(rootKey, t, !weAreAlice);
+		SecretKey inHeaderPrev = deriveHeaderKey(rootKey, t, !weAreAlice);
+		SecretKey outTagPrev = deriveTagKey(rootKey, t, weAreAlice);
+		SecretKey outHeaderPrev = deriveHeaderKey(rootKey, t, weAreAlice);
 		// Derive the keys for the current and next periods
-		SecretKey inTagCurr = rotateKey(inTagPrev, rotationPeriod);
-		SecretKey inHeaderCurr = rotateKey(inHeaderPrev, rotationPeriod);
-		SecretKey inTagNext = rotateKey(inTagCurr, rotationPeriod + 1);
-		SecretKey inHeaderNext = rotateKey(inHeaderCurr, rotationPeriod + 1);
-		SecretKey outTagCurr = rotateKey(outTagPrev, rotationPeriod);
-		SecretKey outHeaderCurr = rotateKey(outHeaderPrev, rotationPeriod);
+		SecretKey inTagCurr = rotateKey(inTagPrev, timePeriod);
+		SecretKey inHeaderCurr = rotateKey(inHeaderPrev, timePeriod);
+		SecretKey inTagNext = rotateKey(inTagCurr, timePeriod + 1);
+		SecretKey inHeaderNext = rotateKey(inHeaderCurr, timePeriod + 1);
+		SecretKey outTagCurr = rotateKey(outTagPrev, timePeriod);
+		SecretKey outHeaderCurr = rotateKey(outHeaderPrev, timePeriod);
 		// Initialise the reordering windows and stream counters
 		IncomingKeys inPrev = new IncomingKeys(inTagPrev, inHeaderPrev,
-				rotationPeriod - 1);
+				timePeriod - 1);
 		IncomingKeys inCurr = new IncomingKeys(inTagCurr, inHeaderCurr,
-				rotationPeriod);
+				timePeriod);
 		IncomingKeys inNext = new IncomingKeys(inTagNext, inHeaderNext,
-				rotationPeriod + 1);
+				timePeriod + 1);
 		OutgoingKeys outCurr = new OutgoingKeys(outTagCurr, outHeaderCurr,
-				rotationPeriod, active);
+				timePeriod, active);
 		// Collect and return the keys
 		return new TransportKeys(t, inPrev, inCurr, inNext, outCurr);
 	}
 
 	@Override
-	public TransportKeys rotateTransportKeys(TransportKeys k,
-			long rotationPeriod) {
-		if (k.getRotationPeriod() >= rotationPeriod) return k;
+	public TransportKeys rotateTransportKeys(TransportKeys k, long timePeriod) {
+		if (k.getTimePeriod() >= timePeriod) return k;
 		IncomingKeys inPrev = k.getPreviousIncomingKeys();
 		IncomingKeys inCurr = k.getCurrentIncomingKeys();
 		IncomingKeys inNext = k.getNextIncomingKeys();
 		OutgoingKeys outCurr = k.getCurrentOutgoingKeys();
-		long startPeriod = outCurr.getRotationPeriod();
+		long startPeriod = outCurr.getTimePeriod();
 		boolean active = outCurr.isActive();
 		// Rotate the keys
-		for (long p = startPeriod + 1; p <= rotationPeriod; p++) {
+		for (long p = startPeriod + 1; p <= timePeriod; p++) {
 			inPrev = inCurr;
 			inCurr = inNext;
 			SecretKey inNextTag = rotateKey(inNext.getTagKey(), p + 1);
@@ -89,24 +95,117 @@ class TransportCryptoImpl implements TransportCrypto {
 				outCurr);
 	}
 
-	private SecretKey rotateKey(SecretKey k, long rotationPeriod) {
+	private SecretKey rotateKey(SecretKey k, long timePeriod) {
 		byte[] period = new byte[INT_64_BYTES];
-		ByteUtils.writeUint64(rotationPeriod, period, 0);
+		writeUint64(timePeriod, period, 0);
 		return crypto.deriveKey(ROTATE_LABEL, k, period);
 	}
 
-	private SecretKey deriveTagKey(SecretKey master, TransportId t,
-			boolean alice) {
-		String label = alice ? ALICE_TAG_LABEL : BOB_TAG_LABEL;
-		byte[] id = StringUtils.toUtf8(t.getString());
-		return crypto.deriveKey(label, master, id);
+	private SecretKey deriveTagKey(SecretKey rootKey, TransportId t,
+			boolean keyBelongsToAlice) {
+		String label = keyBelongsToAlice ? ALICE_TAG_LABEL : BOB_TAG_LABEL;
+		byte[] id = toUtf8(t.getString());
+		return crypto.deriveKey(label, rootKey, id);
 	}
 
-	private SecretKey deriveHeaderKey(SecretKey master, TransportId t,
-			boolean alice) {
-		String label = alice ? ALICE_HEADER_LABEL : BOB_HEADER_LABEL;
-		byte[] id = StringUtils.toUtf8(t.getString());
-		return crypto.deriveKey(label, master, id);
+	private SecretKey deriveHeaderKey(SecretKey rootKey, TransportId t,
+			boolean keyBelongsToAlice) {
+		String label = keyBelongsToAlice ? ALICE_HEADER_LABEL :
+				BOB_HEADER_LABEL;
+		byte[] id = toUtf8(t.getString());
+		return crypto.deriveKey(label, rootKey, id);
+	}
+
+	@Override
+	public HandshakeKeys deriveHandshakeKeys(TransportId t, SecretKey rootKey,
+			long timePeriod, boolean weAreAlice) {
+		if (timePeriod < 1) throw new IllegalArgumentException();
+		IncomingKeys inPrev = deriveIncomingHandshakeKeys(t, rootKey,
+				weAreAlice, timePeriod - 1);
+		IncomingKeys inCurr = deriveIncomingHandshakeKeys(t, rootKey,
+				weAreAlice, timePeriod);
+		IncomingKeys inNext = deriveIncomingHandshakeKeys(t, rootKey,
+				weAreAlice, timePeriod + 1);
+		OutgoingKeys outCurr = deriveOutgoingHandshakeKeys(t, rootKey,
+				weAreAlice, timePeriod);
+		return new HandshakeKeys(t, inPrev, inCurr, inNext, outCurr, rootKey,
+				weAreAlice);
+	}
+
+	private IncomingKeys deriveIncomingHandshakeKeys(TransportId t,
+			SecretKey rootKey, boolean weAreAlice, long timePeriod) {
+		SecretKey tag = deriveHandshakeTagKey(t, rootKey, !weAreAlice,
+				timePeriod);
+		SecretKey header = deriveHandshakeHeaderKey(t, rootKey, !weAreAlice,
+				timePeriod);
+		return new IncomingKeys(tag, header, timePeriod);
+	}
+
+	private OutgoingKeys deriveOutgoingHandshakeKeys(TransportId t,
+			SecretKey rootKey, boolean weAreAlice, long timePeriod) {
+		SecretKey tag = deriveHandshakeTagKey(t, rootKey, weAreAlice,
+				timePeriod);
+		SecretKey header = deriveHandshakeHeaderKey(t, rootKey, weAreAlice,
+				timePeriod);
+		return new OutgoingKeys(tag, header, timePeriod, true);
+	}
+
+	private SecretKey deriveHandshakeTagKey(TransportId t, SecretKey rootKey,
+			boolean keyBelongsToAlice, long timePeriod) {
+		String label = keyBelongsToAlice ? ALICE_HANDSHAKE_TAG_LABEL :
+				BOB_HANDSHAKE_TAG_LABEL;
+		byte[] id = toUtf8(t.getString());
+		byte[] period = new byte[INT_64_BYTES];
+		writeUint64(timePeriod, period, 0);
+		return crypto.deriveKey(label, rootKey, id, period);
+	}
+
+	private SecretKey deriveHandshakeHeaderKey(TransportId t, SecretKey rootKey,
+			boolean keyBelongsToAlice, long timePeriod) {
+		String label = keyBelongsToAlice ? ALICE_HANDSHAKE_HEADER_LABEL :
+				BOB_HANDSHAKE_HEADER_LABEL;
+		byte[] id = toUtf8(t.getString());
+		byte[] period = new byte[INT_64_BYTES];
+		writeUint64(timePeriod, period, 0);
+		return crypto.deriveKey(label, rootKey, id, period);
+	}
+
+	@Override
+	public HandshakeKeys updateHandshakeKeys(HandshakeKeys k, long timePeriod) {
+		long elapsed = timePeriod - k.getTimePeriod();
+		TransportId t = k.getTransportId();
+		SecretKey rootKey = k.getRootKey();
+		boolean weAreAlice = k.isAlice();
+		if (elapsed <= 0) {
+			// The keys are for the given period or later - don't update them
+			return k;
+		} else if (elapsed == 1) {
+			// The keys are one period old - shift by one period, keeping the
+			// reordering windows for keys we retain
+			IncomingKeys inPrev = k.getCurrentIncomingKeys();
+			IncomingKeys inCurr = k.getNextIncomingKeys();
+			IncomingKeys inNext = deriveIncomingHandshakeKeys(t, rootKey,
+					weAreAlice, timePeriod + 1);
+			OutgoingKeys outCurr = deriveOutgoingHandshakeKeys(t, rootKey,
+					weAreAlice, timePeriod);
+			return new HandshakeKeys(t, inPrev, inCurr, inNext, outCurr,
+					rootKey, weAreAlice);
+		} else if (elapsed == 2) {
+			// The keys are two periods old - shift by two periods, keeping
+			// the reordering windows for keys we retain
+			IncomingKeys inPrev = k.getNextIncomingKeys();
+			IncomingKeys inCurr = deriveIncomingHandshakeKeys(t, rootKey,
+					weAreAlice, timePeriod);
+			IncomingKeys inNext = deriveIncomingHandshakeKeys(t, rootKey,
+					weAreAlice, timePeriod + 1);
+			OutgoingKeys outCurr = deriveOutgoingHandshakeKeys(t, rootKey,
+					weAreAlice, timePeriod);
+			return new HandshakeKeys(t, inPrev, inCurr, inNext, outCurr,
+					rootKey, weAreAlice);
+		} else {
+			// The keys are more than two periods old - derive fresh keys
+			return deriveHandshakeKeys(t, rootKey, timePeriod, weAreAlice);
+		}
 	}
 
 	@Override
@@ -125,14 +224,14 @@ class TransportCryptoImpl implements TransportCrypto {
 		// The input is the protocol version as a 16-bit integer, followed by
 		// the stream number as a 64-bit integer
 		byte[] protocolVersionBytes = new byte[INT_16_BYTES];
-		ByteUtils.writeUint16(protocolVersion, protocolVersionBytes, 0);
+		writeUint16(protocolVersion, protocolVersionBytes, 0);
 		prf.update(protocolVersionBytes, 0, protocolVersionBytes.length);
 		byte[] streamNumberBytes = new byte[INT_64_BYTES];
-		ByteUtils.writeUint64(streamNumber, streamNumberBytes, 0);
+		writeUint64(streamNumber, streamNumberBytes, 0);
 		prf.update(streamNumberBytes, 0, streamNumberBytes.length);
 		byte[] mac = new byte[macLength];
 		prf.doFinal(mac, 0);
 		// The output is the first TAG_LENGTH bytes of the MAC
-		System.arraycopy(mac, 0, tag, 0, TAG_LENGTH);
+		arraycopy(mac, 0, tag, 0, TAG_LENGTH);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/db/Database.java

@@ -2,16 +2,20 @@ package org.briarproject.bramble.db;
 
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.contact.PendingContactState;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DataTooNewException;
 import org.briarproject.bramble.api.db.DataTooOldException;
+import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MessageDeletedException;
 import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorId;
-import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.identity.Identity;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.settings.Settings;
@@ -23,8 +27,11 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.validation.MessageState;
-import org.briarproject.bramble.api.transport.KeySet;
-import org.briarproject.bramble.api.transport.KeySetId;
+import org.briarproject.bramble.api.transport.HandshakeKeySet;
+import org.briarproject.bramble.api.transport.HandshakeKeySetId;
+import org.briarproject.bramble.api.transport.HandshakeKeys;
+import org.briarproject.bramble.api.transport.TransportKeySet;
+import org.briarproject.bramble.api.transport.TransportKeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.Collection;
@@ -33,11 +40,14 @@ import java.util.Map;
 import javax.annotation.Nullable;
 
 /**
- * A low-level interface to the database (DatabaseComponent provides a
- * high-level interface). Most operations take a transaction argument, which is
- * obtained by calling {@link #startTransaction()}. Every transaction must be
- * terminated by calling either {@link #abortTransaction(Object) abortTransaction(T)} or
- * {@link #commitTransaction(Object) commitTransaction(T)}, even if an exception is thrown.
+ * A low-level interface to the database ({@link DatabaseComponent} provides a
+ * high-level interface).
+ * <p/>
+ * Most operations take a transaction argument, which is obtained by calling
+ * {@link #startTransaction()}. Every transaction must be terminated by calling
+ * either {@link #abortTransaction(Object) abortTransaction(T)} or
+ * {@link #commitTransaction(Object) commitTransaction(T)}, even if an
+ * exception is thrown.
  */
 @NotNullByDefault
 interface Database<T> {
@@ -80,8 +90,8 @@ interface Database<T> {
 	 * Stores a contact associated with the given local and remote pseudonyms,
 	 * and returns an ID for the contact.
 	 */
-	ContactId addContact(T txn, Author remote, AuthorId local, boolean verified,
-			boolean active) throws DbException;
+	ContactId addContact(T txn, Author remote, AuthorId local, boolean verified)
+			throws DbException;
 
 	/**
 	 * Stores a group.
@@ -96,9 +106,23 @@ interface Database<T> {
 			throws DbException;
 
 	/**
-	 * Stores a local pseudonym.
+	 * Stores the given handshake keys for the given contact and returns a
+	 * key set ID.
 	 */
-	void addLocalAuthor(T txn, LocalAuthor a) throws DbException;
+	HandshakeKeySetId addHandshakeKeys(T txn, ContactId c, HandshakeKeys k)
+			throws DbException;
+
+	/**
+	 * Stores the given handshake keys for the given pending contact and
+	 * returns a key set ID.
+	 */
+	HandshakeKeySetId addHandshakeKeys(T txn, PendingContactId p,
+			HandshakeKeys k) throws DbException;
+
+	/**
+	 * Stores an identity.
+	 */
+	void addIdentity(T txn, Identity i) throws DbException;
 
 	/**
 	 * Stores a message.
@@ -121,6 +145,11 @@ interface Database<T> {
 	 */
 	void addOfferedMessage(T txn, ContactId c, MessageId m) throws DbException;
 
+	/**
+	 * Stores a pending contact.
+	 */
+	void addPendingContact(T txn, PendingContact p) throws DbException;
+
 	/**
 	 * Stores a transport.
 	 */
@@ -131,7 +160,7 @@ interface Database<T> {
 	 * Stores the given transport keys for the given contact and returns a
 	 * key set ID.
 	 */
-	KeySetId addTransportKeys(T txn, ContactId c, TransportKeys k)
+	TransportKeySetId addTransportKeys(T txn, ContactId c, TransportKeys k)
 			throws DbException;
 
 	/**
@@ -158,11 +187,12 @@ interface Database<T> {
 	boolean containsGroup(T txn, GroupId g) throws DbException;
 
 	/**
-	 * Returns true if the database contains the given local pseudonym.
+	 * Returns true if the database contains an identity for the given
+	 * pseudonym.
 	 * <p/>
 	 * Read-only.
 	 */
-	boolean containsLocalAuthor(T txn, AuthorId a) throws DbException;
+	boolean containsIdentity(T txn, AuthorId a) throws DbException;
 
 	/**
 	 * Returns true if the database contains the given message.
@@ -171,6 +201,14 @@ interface Database<T> {
 	 */
 	boolean containsMessage(T txn, MessageId m) throws DbException;
 
+	/**
+	 * Returns true if the database contains the given pending contact.
+	 * <p/>
+	 * Read-only.
+	 */
+	boolean containsPendingContact(T txn, PendingContactId p)
+			throws DbException;
+
 	/**
 	 * Returns true if the database contains the given transport.
 	 * <p/>
@@ -237,13 +275,6 @@ interface Database<T> {
 	 */
 	Collection<ContactId> getContacts(T txn, AuthorId a) throws DbException;
 
-	/**
-	 * Returns the amount of free storage space available to the database, in
-	 * bytes. This is based on the minimum of the space available on the device
-	 * where the database is stored and the database's configured size.
-	 */
-	long getFreeSpace() throws DbException;
-
 	/**
 	 * Returns the group with the given ID.
 	 * <p/>
@@ -285,18 +316,26 @@ interface Database<T> {
 			throws DbException;
 
 	/**
-	 * Returns the local pseudonym with the given ID.
+	 * Returns all handshake keys for the given transport.
 	 * <p/>
 	 * Read-only.
 	 */
-	LocalAuthor getLocalAuthor(T txn, AuthorId a) throws DbException;
+	Collection<HandshakeKeySet> getHandshakeKeys(T txn, TransportId t)
+			throws DbException;
 
 	/**
-	 * Returns all local pseudonyms.
+	 * Returns the identity for local pseudonym with the given ID.
 	 * <p/>
 	 * Read-only.
 	 */
-	Collection<LocalAuthor> getLocalAuthors(T txn) throws DbException;
+	Identity getIdentity(T txn, AuthorId a) throws DbException;
+
+	/**
+	 * Returns the identities for all local pseudonyms.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<Identity> getIdentities(T txn) throws DbException;
 
 	/**
 	 * Returns the message with the given ID.
@@ -474,6 +513,13 @@ interface Database<T> {
 	 */
 	long getNextSendTime(T txn, ContactId c) throws DbException;
 
+	/**
+	 * Returns all pending contacts.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<PendingContact> getPendingContacts(T txn) throws DbException;
+
 	/**
 	 * Returns the IDs of some messages that are eligible to be sent to the
 	 * given contact and have been requested by the contact, up to the given
@@ -496,13 +542,19 @@ interface Database<T> {
 	 * <p/>
 	 * Read-only.
 	 */
-	Collection<KeySet> getTransportKeys(T txn, TransportId t)
+	Collection<TransportKeySet> getTransportKeys(T txn, TransportId t)
+			throws DbException;
+
+	/**
+	 * Increments the outgoing stream counter for the given handshake keys.
+	 */
+	void incrementStreamCounter(T txn, TransportId t, HandshakeKeySetId k)
 			throws DbException;
 
 	/**
 	 * Increments the outgoing stream counter for the given transport keys.
 	 */
-	void incrementStreamCounter(T txn, TransportId t, KeySetId k)
+	void incrementStreamCounter(T txn, TransportId t, TransportKeySetId k)
 			throws DbException;
 
 	/**
@@ -572,9 +624,15 @@ interface Database<T> {
 			throws DbException;
 
 	/**
-	 * Removes a local pseudonym (and all associated state) from the database.
+	 * Removes the given handshake keys from the database.
 	 */
-	void removeLocalAuthor(T txn, AuthorId a) throws DbException;
+	void removeHandshakeKeys(T txn, TransportId t, HandshakeKeySetId k)
+			throws DbException;
+
+	/**
+	 * Removes an identity (and all associated state) from the database.
+	 */
+	void removeIdentity(T txn, AuthorId a) throws DbException;
 
 	/**
 	 * Removes a message (and all associated state) from the database.
@@ -588,6 +646,11 @@ interface Database<T> {
 	void removeOfferedMessages(T txn, ContactId c,
 			Collection<MessageId> requested) throws DbException;
 
+	/**
+	 * Removes a pending contact (and all associated state) from the database.
+	 */
+	void removePendingContact(T txn, PendingContactId p) throws DbException;
+
 	/**
 	 * Removes a transport (and all associated state) from the database.
 	 */
@@ -596,7 +659,7 @@ interface Database<T> {
 	/**
 	 * Removes the given transport keys from the database.
 	 */
-	void removeTransportKeys(T txn, TransportId t, KeySetId k)
+	void removeTransportKeys(T txn, TransportId t, TransportKeySetId k)
 			throws DbException;
 
 	/**
@@ -610,12 +673,6 @@ interface Database<T> {
 	 */
 	void setContactVerified(T txn, ContactId c) throws DbException;
 
-	/**
-	 * Marks the given contact as active or inactive.
-	 */
-	void setContactActive(T txn, ContactId c, boolean active)
-			throws DbException;
-
 	/**
 	 * Sets an alias name for a contact.
 	 */
@@ -629,6 +686,12 @@ interface Database<T> {
 	void setGroupVisibility(T txn, ContactId c, GroupId g, boolean shared)
 			throws DbException;
 
+	/**
+	 * Sets the handshake key pair for the identity with the given ID.
+	 */
+	void setHandshakeKeyPair(T txn, AuthorId local, byte[] publicKey,
+			byte[] privateKey) throws DbException;
+
 	/**
 	 * Marks the given message as shared.
 	 */
@@ -641,16 +704,29 @@ interface Database<T> {
 			throws DbException;
 
 	/**
-	 * Sets the reordering window for the given key set and transport in the
-	 * given rotation period.
+	 * Sets the state of the given pending contact.
 	 */
-	void setReorderingWindow(T txn, KeySetId k, TransportId t,
-			long rotationPeriod, long base, byte[] bitmap) throws DbException;
+	void setPendingContactState(T txn, PendingContactId p,
+			PendingContactState state) throws DbException;
+
+	/**
+	 * Sets the reordering window for the given transport key set in the given
+	 * time period.
+	 */
+	void setReorderingWindow(T txn, TransportKeySetId k, TransportId t,
+			long timePeriod, long base, byte[] bitmap) throws DbException;
+
+	/**
+	 * Sets the reordering window for the given handshake key set in the given
+	 * time period.
+	 */
+	void setReorderingWindow(T txn, HandshakeKeySetId k, TransportId t,
+			long timePeriod, long base, byte[] bitmap) throws DbException;
 
 	/**
 	 * Marks the given transport keys as usable for outgoing streams.
 	 */
-	void setTransportKeysActive(T txn, TransportId t, KeySetId k)
+	void setTransportKeysActive(T txn, TransportId t, TransportKeySetId k)
 			throws DbException;
 
 	/**
@@ -661,8 +737,13 @@ interface Database<T> {
 	void updateExpiryTimeAndEta(T txn, ContactId c, MessageId m, int maxLatency)
 			throws DbException;
 
+	/**
+	 * Updates the given handshake keys.
+	 */
+	void updateHandshakeKeys(T txn, HandshakeKeySet ks) throws DbException;
+
 	/**
 	 * Updates the given transport keys following key rotation.
 	 */
-	void updateTransportKeys(T txn, KeySet ks) throws DbException;
+	void updateTransportKeys(T txn, TransportKeySet ks) throws DbException;
 }

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseComponentImpl.java

@@ -2,32 +2,39 @@ package org.briarproject.bramble.db;
 
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.contact.event.ContactAddedEvent;
 import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
-import org.briarproject.bramble.api.contact.event.ContactStatusChangedEvent;
 import org.briarproject.bramble.api.contact.event.ContactVerifiedEvent;
 import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.db.CommitAction;
+import org.briarproject.bramble.api.db.CommitAction.Visitor;
 import org.briarproject.bramble.api.db.ContactExistsException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbCallable;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.DbRunnable;
+import org.briarproject.bramble.api.db.EventAction;
 import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.db.NoSuchContactException;
 import org.briarproject.bramble.api.db.NoSuchGroupException;
-import org.briarproject.bramble.api.db.NoSuchLocalAuthorException;
+import org.briarproject.bramble.api.db.NoSuchIdentityException;
 import org.briarproject.bramble.api.db.NoSuchMessageException;
+import org.briarproject.bramble.api.db.NoSuchPendingContactException;
 import org.briarproject.bramble.api.db.NoSuchTransportException;
 import org.briarproject.bramble.api.db.NullableDbCallable;
+import org.briarproject.bramble.api.db.PendingContactExistsException;
+import org.briarproject.bramble.api.db.TaskAction;
 import org.briarproject.bramble.api.db.Transaction;
-import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorId;
-import org.briarproject.bramble.api.identity.LocalAuthor;
-import org.briarproject.bramble.api.identity.event.LocalAuthorAddedEvent;
-import org.briarproject.bramble.api.identity.event.LocalAuthorRemovedEvent;
+import org.briarproject.bramble.api.identity.Identity;
+import org.briarproject.bramble.api.identity.event.IdentityAddedEvent;
+import org.briarproject.bramble.api.identity.event.IdentityRemovedEvent;
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
@@ -55,8 +62,11 @@ import org.briarproject.bramble.api.sync.event.MessageToRequestEvent;
 import org.briarproject.bramble.api.sync.event.MessagesAckedEvent;
 import org.briarproject.bramble.api.sync.event.MessagesSentEvent;
 import org.briarproject.bramble.api.sync.validation.MessageState;
-import org.briarproject.bramble.api.transport.KeySet;
-import org.briarproject.bramble.api.transport.KeySetId;
+import org.briarproject.bramble.api.transport.HandshakeKeySet;
+import org.briarproject.bramble.api.transport.HandshakeKeySetId;
+import org.briarproject.bramble.api.transport.HandshakeKeys;
+import org.briarproject.bramble.api.transport.TransportKeySet;
+import org.briarproject.bramble.api.transport.TransportKeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
 
 import java.util.ArrayList;
@@ -64,6 +74,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.logging.Logger;
@@ -92,25 +103,29 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	private final Database<T> db;
 	private final Class<T> txnClass;
 	private final EventBus eventBus;
-	private final ShutdownManager shutdown;
+	private final Executor eventExecutor;
+	private final ShutdownManager shutdownManager;
 	private final AtomicBoolean closed = new AtomicBoolean(false);
 	private final ReentrantReadWriteLock lock =
 			new ReentrantReadWriteLock(true);
+	private final Visitor visitor = new CommitActionVisitor();
 
 	@Inject
 	DatabaseComponentImpl(Database<T> db, Class<T> txnClass, EventBus eventBus,
-			ShutdownManager shutdown) {
+			@EventExecutor Executor eventExecutor,
+			ShutdownManager shutdownManager) {
 		this.db = db;
 		this.txnClass = txnClass;
 		this.eventBus = eventBus;
-		this.shutdown = shutdown;
+		this.eventExecutor = eventExecutor;
+		this.shutdownManager = shutdownManager;
 	}
 
 	@Override
 	public boolean open(SecretKey key, @Nullable MigrationListener listener)
 			throws DbException {
 		boolean reopened = db.open(key, listener);
-		shutdown.addShutdownHook(() -> {
+		shutdownManager.addShutdownHook(() -> {
 			try {
 				close();
 			} catch (DbException e) {
@@ -160,13 +175,16 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	public void endTransaction(Transaction transaction) {
 		try {
 			T txn = txnClass.cast(transaction.unbox());
-			if (!transaction.isCommitted()) db.abortTransaction(txn);
+			if (transaction.isCommitted()) {
+				for (CommitAction a : transaction.getActions())
+					a.accept(visitor);
+			} else {
+				db.abortTransaction(txn);
+			}
 		} finally {
 			if (transaction.isReadOnly()) lock.readLock().unlock();
 			else lock.writeLock().unlock();
 		}
-		if (transaction.isCommitted())
-			for (Event e : transaction.getEvents()) eventBus.broadcast(e);
 	}
 
 	@Override
@@ -215,19 +233,18 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 
 	@Override
 	public ContactId addContact(Transaction transaction, Author remote,
-			AuthorId local, boolean verified, boolean active)
+			AuthorId local, boolean verified)
 			throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
-		if (!db.containsLocalAuthor(txn, local))
-			throw new NoSuchLocalAuthorException();
-		if (db.containsLocalAuthor(txn, remote.getId()))
+		if (!db.containsIdentity(txn, local))
+			throw new NoSuchIdentityException();
+		if (db.containsIdentity(txn, remote.getId()))
 			throw new ContactExistsException();
 		if (db.containsContact(txn, remote.getId(), local))
 			throw new ContactExistsException();
-		ContactId c = db.addContact(txn, remote, local, verified, active);
-		transaction.attach(new ContactAddedEvent(c, active));
-		if (active) transaction.attach(new ContactStatusChangedEvent(c, true));
+		ContactId c = db.addContact(txn, remote, local, verified);
+		transaction.attach(new ContactAddedEvent(c));
 		return c;
 	}
 
@@ -242,13 +259,37 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public void addLocalAuthor(Transaction transaction, LocalAuthor a)
+	public HandshakeKeySetId addHandshakeKeys(Transaction transaction,
+			ContactId c, HandshakeKeys k) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		if (!db.containsTransport(txn, k.getTransportId()))
+			throw new NoSuchTransportException();
+		return db.addHandshakeKeys(txn, c, k);
+	}
+
+	@Override
+	public HandshakeKeySetId addHandshakeKeys(Transaction transaction,
+			PendingContactId p, HandshakeKeys k) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsPendingContact(txn, p))
+			throw new NoSuchPendingContactException();
+		if (!db.containsTransport(txn, k.getTransportId()))
+			throw new NoSuchTransportException();
+		return db.addHandshakeKeys(txn, p, k);
+	}
+
+	@Override
+	public void addIdentity(Transaction transaction, Identity i)
 			throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
-		if (!db.containsLocalAuthor(txn, a.getId())) {
-			db.addLocalAuthor(txn, a);
-			transaction.attach(new LocalAuthorAddedEvent(a.getId()));
+		if (!db.containsIdentity(txn, i.getId())) {
+			db.addIdentity(txn, i);
+			transaction.attach(new IdentityAddedEvent(i.getId()));
 		}
 	}
 
@@ -269,6 +310,16 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		db.mergeMessageMetadata(txn, m.getId(), meta);
 	}
 
+	@Override
+	public void addPendingContact(Transaction transaction, PendingContact p)
+			throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (db.containsPendingContact(txn, p.getId()))
+			throw new PendingContactExistsException();
+		db.addPendingContact(txn, p);
+	}
+
 	@Override
 	public void addTransport(Transaction transaction, TransportId t,
 			int maxLatency) throws DbException {
@@ -279,8 +330,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public KeySetId addTransportKeys(Transaction transaction, ContactId c,
-			TransportKeys k) throws DbException {
+	public TransportKeySetId addTransportKeys(Transaction transaction,
+			ContactId c, TransportKeys k) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
@@ -294,8 +345,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	public boolean containsContact(Transaction transaction, AuthorId remote,
 			AuthorId local) throws DbException {
 		T txn = unbox(transaction);
-		if (!db.containsLocalAuthor(txn, local))
-			throw new NoSuchLocalAuthorException();
+		if (!db.containsIdentity(txn, local))
+			throw new NoSuchIdentityException();
 		return db.containsContact(txn, remote, local);
 	}
 
@@ -307,10 +358,17 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public boolean containsLocalAuthor(Transaction transaction, AuthorId local)
+	public boolean containsIdentity(Transaction transaction, AuthorId a)
 			throws DbException {
 		T txn = unbox(transaction);
-		return db.containsLocalAuthor(txn, local);
+		return db.containsIdentity(txn, a);
+	}
+
+	@Override
+	public boolean containsPendingContact(Transaction transaction,
+			PendingContactId p) throws DbException {
+		T txn = unbox(transaction);
+		return db.containsPendingContact(txn, p);
 	}
 
 	@Override
@@ -447,8 +505,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	public Collection<ContactId> getContacts(Transaction transaction,
 			AuthorId a) throws DbException {
 		T txn = unbox(transaction);
-		if (!db.containsLocalAuthor(txn, a))
-			throw new NoSuchLocalAuthorException();
+		if (!db.containsIdentity(txn, a))
+			throw new NoSuchIdentityException();
 		return db.getContacts(txn, a);
 	}
 
@@ -487,19 +545,28 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public LocalAuthor getLocalAuthor(Transaction transaction, AuthorId a)
-			throws DbException {
+	public Collection<HandshakeKeySet> getHandshakeKeys(Transaction transaction,
+			TransportId t) throws DbException {
 		T txn = unbox(transaction);
-		if (!db.containsLocalAuthor(txn, a))
-			throw new NoSuchLocalAuthorException();
-		return db.getLocalAuthor(txn, a);
+		if (!db.containsTransport(txn, t))
+			throw new NoSuchTransportException();
+		return db.getHandshakeKeys(txn, t);
 	}
 
 	@Override
-	public Collection<LocalAuthor> getLocalAuthors(Transaction transaction)
+	public Identity getIdentity(Transaction transaction, AuthorId a)
 			throws DbException {
 		T txn = unbox(transaction);
-		return db.getLocalAuthors(txn);
+		if (!db.containsIdentity(txn, a))
+			throw new NoSuchIdentityException();
+		return db.getIdentity(txn, a);
+	}
+
+	@Override
+	public Collection<Identity> getIdentities(Transaction transaction)
+			throws DbException {
+		T txn = unbox(transaction);
+		return db.getIdentities(txn);
 	}
 
 	@Override
@@ -643,6 +710,13 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.getNextSendTime(txn, c);
 	}
 
+	@Override
+	public Collection<PendingContact> getPendingContacts(
+			Transaction transaction) throws DbException {
+		T txn = unbox(transaction);
+		return db.getPendingContacts(txn);
+	}
+
 	@Override
 	public Settings getSettings(Transaction transaction, String namespace)
 			throws DbException {
@@ -651,7 +725,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Collection<KeySet> getTransportKeys(Transaction transaction,
+	public Collection<TransportKeySet> getTransportKeys(Transaction transaction,
 			TransportId t) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsTransport(txn, t))
@@ -661,7 +735,17 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 
 	@Override
 	public void incrementStreamCounter(Transaction transaction, TransportId t,
-			KeySetId k) throws DbException {
+			HandshakeKeySetId k) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsTransport(txn, t))
+			throw new NoSuchTransportException();
+		db.incrementStreamCounter(txn, t, k);
+	}
+
+	@Override
+	public void incrementStreamCounter(Transaction transaction, TransportId t,
+			TransportKeySetId k) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsTransport(txn, t))
@@ -811,14 +895,24 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public void removeLocalAuthor(Transaction transaction, AuthorId a)
+	public void removeHandshakeKeys(Transaction transaction,
+			TransportId t, HandshakeKeySetId k) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsTransport(txn, t))
+			throw new NoSuchTransportException();
+		db.removeHandshakeKeys(txn, t, k);
+	}
+
+	@Override
+	public void removeIdentity(Transaction transaction, AuthorId a)
 			throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
-		if (!db.containsLocalAuthor(txn, a))
-			throw new NoSuchLocalAuthorException();
-		db.removeLocalAuthor(txn, a);
-		transaction.attach(new LocalAuthorRemovedEvent(a));
+		if (!db.containsIdentity(txn, a))
+			throw new NoSuchIdentityException();
+		db.removeIdentity(txn, a);
+		transaction.attach(new IdentityRemovedEvent(a));
 	}
 
 	@Override
@@ -832,6 +926,16 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		db.removeMessage(txn, m);
 	}
 
+	@Override
+	public void removePendingContact(Transaction transaction,
+			PendingContactId p) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsPendingContact(txn, p))
+			throw new NoSuchPendingContactException();
+		db.removePendingContact(txn, p);
+	}
+
 	@Override
 	public void removeTransport(Transaction transaction, TransportId t)
 			throws DbException {
@@ -844,7 +948,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 
 	@Override
 	public void removeTransportKeys(Transaction transaction,
-			TransportId t, KeySetId k) throws DbException {
+			TransportId t, TransportKeySetId k) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsTransport(txn, t))
@@ -863,17 +967,6 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		transaction.attach(new ContactVerifiedEvent(c));
 	}
 
-	@Override
-	public void setContactActive(Transaction transaction, ContactId c,
-			boolean active) throws DbException {
-		if (transaction.isReadOnly()) throw new IllegalArgumentException();
-		T txn = unbox(transaction);
-		if (!db.containsContact(txn, c))
-			throw new NoSuchContactException();
-		db.setContactActive(txn, c, active);
-		transaction.attach(new ContactStatusChangedEvent(c, active));
-	}
-
 	@Override
 	public void setContactAlias(Transaction transaction, ContactId c,
 			@Nullable String alias) throws DbException {
@@ -943,19 +1036,40 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public void setReorderingWindow(Transaction transaction, KeySetId k,
-			TransportId t, long rotationPeriod, long base, byte[] bitmap)
-			throws DbException {
+	public void setHandshakeKeyPair(Transaction transaction, AuthorId local,
+			byte[] publicKey, byte[] privateKey) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsIdentity(txn, local))
+			throw new NoSuchIdentityException();
+		db.setHandshakeKeyPair(txn, local, publicKey, privateKey);
+	}
+
+	@Override
+	public void setReorderingWindow(Transaction transaction,
+			TransportKeySetId k, TransportId t, long timePeriod, long base,
+			byte[] bitmap) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsTransport(txn, t))
 			throw new NoSuchTransportException();
-		db.setReorderingWindow(txn, k, t, rotationPeriod, base, bitmap);
+		db.setReorderingWindow(txn, k, t, timePeriod, base, bitmap);
+	}
+
+	@Override
+	public void setReorderingWindow(Transaction transaction,
+			HandshakeKeySetId k, TransportId t, long timePeriod, long base,
+			byte[] bitmap) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsTransport(txn, t))
+			throw new NoSuchTransportException();
+		db.setReorderingWindow(txn, k, t, timePeriod, base, bitmap);
 	}
 
 	@Override
 	public void setTransportKeysActive(Transaction transaction, TransportId t,
-			KeySetId k) throws DbException {
+			TransportKeySetId k) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsTransport(txn, t))
@@ -964,14 +1078,39 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public void updateTransportKeys(Transaction transaction,
-			Collection<KeySet> keys) throws DbException {
+	public void updateHandshakeKeys(Transaction transaction,
+			Collection<HandshakeKeySet> keys) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
-		for (KeySet ks : keys) {
-			TransportId t = ks.getTransportKeys().getTransportId();
+		for (HandshakeKeySet ks : keys) {
+			TransportId t = ks.getKeys().getTransportId();
+			if (db.containsTransport(txn, t))
+				db.updateHandshakeKeys(txn, ks);
+		}
+	}
+
+	@Override
+	public void updateTransportKeys(Transaction transaction,
+			Collection<TransportKeySet> keys) throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		for (TransportKeySet ks : keys) {
+			TransportId t = ks.getKeys().getTransportId();
 			if (db.containsTransport(txn, t))
 				db.updateTransportKeys(txn, ks);
 		}
 	}
+
+	private class CommitActionVisitor implements Visitor {
+
+		@Override
+		public void visit(EventAction a) {
+			eventBus.broadcast(a.getEvent());
+		}
+
+		@Override
+		public void visit(TaskAction a) {
+			eventExecutor.execute(a.getTask());
+		}
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseModule.java

@@ -3,11 +3,13 @@ package org.briarproject.bramble.db;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.system.Clock;
 
 import java.sql.Connection;
+import java.util.concurrent.Executor;
 
 import javax.inject.Singleton;
 
@@ -27,8 +29,9 @@ public class DatabaseModule {
 	@Provides
 	@Singleton
 	DatabaseComponent provideDatabaseComponent(Database<Connection> db,
-			EventBus eventBus, ShutdownManager shutdown) {
+			EventBus eventBus, @EventExecutor Executor eventExecutor,
+			ShutdownManager shutdownManager) {
 		return new DatabaseComponentImpl<>(db, Connection.class, eventBus,
-				shutdown);
+				eventExecutor, shutdownManager);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/db/H2Database.java

@@ -76,30 +76,6 @@ class H2Database extends JdbcDatabase {
 		}
 	}
 
-	@Override
-	public long getFreeSpace() {
-		File dir = config.getDatabaseDirectory();
-		long maxSize = config.getMaxSize();
-		long free = dir.getFreeSpace();
-		long used = getDiskSpace(dir);
-		long quota = maxSize - used;
-		return Math.min(free, quota);
-	}
-
-	private long getDiskSpace(File f) {
-		if (f.isDirectory()) {
-			long total = 0;
-			File[] children = f.listFiles();
-			if (children != null)
-				for (File child : children) total += getDiskSpace(child);
-			return total;
-		} else if (f.isFile()) {
-			return f.length();
-		} else {
-			return 0;
-		}
-	}
-
 	@Override
 	protected Connection createConnection() throws SQLException {
 		SecretKey key = this.key;

bramble-core/src/main/java/org/briarproject/bramble/db/HyperSqlDatabase.java

@@ -86,30 +86,6 @@ class HyperSqlDatabase extends JdbcDatabase {
 		}
 	}
 
-	@Override
-	public long getFreeSpace() {
-		File dir = config.getDatabaseDirectory();
-		long maxSize = config.getMaxSize();
-		long free = dir.getFreeSpace();
-		long used = getDiskSpace(dir);
-		long quota = maxSize - used;
-		return Math.min(free, quota);
-	}
-
-	private long getDiskSpace(File f) {
-		if (f.isDirectory()) {
-			long total = 0;
-			File[] children = f.listFiles();
-			if (children != null)
-				for (File child : children) total += getDiskSpace(child);
-			return total;
-		} else if (f.isFile()) {
-			return f.length();
-		} else {
-			return 0;
-		}
-	}
-
 	@Override
 	protected Connection createConnection() throws SQLException {
 		SecretKey key = this.key;

bramble-core/src/main/java/org/briarproject/bramble/db/Migration40_41.java

@@ -17,7 +17,7 @@ class Migration40_41 implements Migration<Connection> {
 
 	private final DatabaseTypes dbTypes;
 
-	public Migration40_41(DatabaseTypes databaseTypes) {
+	Migration40_41(DatabaseTypes databaseTypes) {
 		this.dbTypes = databaseTypes;
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/db/Migration41_42.java

@@ -0,0 +1,97 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.db.DbException;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
+class Migration41_42 implements Migration<Connection> {
+
+	private static final Logger LOG = getLogger(Migration41_42.class.getName());
+
+	private final DatabaseTypes dbTypes;
+
+	Migration41_42(DatabaseTypes dbTypes) {
+		this.dbTypes = dbTypes;
+	}
+
+	@Override
+	public int getStartVersion() {
+		return 41;
+	}
+
+	@Override
+	public int getEndVersion() {
+		return 42;
+	}
+
+	@Override
+	public void migrate(Connection txn) throws DbException {
+		Statement s = null;
+		try {
+			s = txn.createStatement();
+			s.execute("ALTER TABLE outgoingKeys"
+					+ " ALTER COLUMN rotationPeriod"
+					+ " RENAME TO timePeriod");
+			s.execute("ALTER TABLE incomingKeys"
+					+ " ALTER COLUMN rotationPeriod"
+					+ " RENAME TO timePeriod");
+			s.execute("ALTER TABLE incomingKeys"
+					+ " DROP COLUMN contactId");
+			s.execute(dbTypes.replaceTypes("CREATE TABLE pendingContacts"
+					+ " (pendingContactId _HASH NOT NULL,"
+					+ " publicKey _BINARY NOT NULL,"
+					+ " alias _STRING NOT NULL,"
+					+ " state INT NOT NULL,"
+					+ " timestamp BIGINT NOT NULL,"
+					+ " PRIMARY KEY (pendingContactId))"));
+			s.execute(dbTypes.replaceTypes("CREATE TABLE outgoingHandshakeKeys"
+					+ " (transportId _STRING NOT NULL,"
+					+ " keySetId _COUNTER,"
+					+ " timePeriod BIGINT NOT NULL,"
+					+ " contactId INT," // Null if contact is pending
+					+ " pendingContactId _HASH," // Null if not pending
+					+ " rootKey _SECRET NOT NULL,"
+					+ " alice BOOLEAN NOT NULL,"
+					+ " tagKey _SECRET NOT NULL,"
+					+ " headerKey _SECRET NOT NULL,"
+					+ " stream BIGINT NOT NULL,"
+					+ " PRIMARY KEY (transportId, keySetId),"
+					+ " FOREIGN KEY (transportId)"
+					+ " REFERENCES transports (transportId)"
+					+ " ON DELETE CASCADE,"
+					+ " UNIQUE (keySetId),"
+					+ " FOREIGN KEY (contactId)"
+					+ " REFERENCES contacts (contactId)"
+					+ " ON DELETE CASCADE,"
+					+ " FOREIGN KEY (pendingContactId)"
+					+ " REFERENCES pendingContacts (pendingContactId)"
+					+ " ON DELETE CASCADE)"));
+			s.execute(dbTypes.replaceTypes("CREATE TABLE incomingHandshakeKeys"
+					+ " (transportId _STRING NOT NULL,"
+					+ " keySetId INT NOT NULL,"
+					+ " timePeriod BIGINT NOT NULL,"
+					+ " tagKey _SECRET NOT NULL,"
+					+ " headerKey _SECRET NOT NULL,"
+					+ " base BIGINT NOT NULL,"
+					+ " bitmap _BINARY NOT NULL,"
+					+ " periodOffset INT NOT NULL,"
+					+ " PRIMARY KEY (transportId, keySetId, periodOffset),"
+					+ " FOREIGN KEY (transportId)"
+					+ " REFERENCES transports (transportId)"
+					+ " ON DELETE CASCADE,"
+					+ " FOREIGN KEY (keySetId)"
+					+ " REFERENCES outgoingHandshakeKeys (keySetId)"
+					+ " ON DELETE CASCADE)"));
+		} catch (SQLException e) {
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/db/Migration42_43.java

@@ -0,0 +1,52 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.db.DbException;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
+class Migration42_43 implements Migration<Connection> {
+
+	private static final Logger LOG = getLogger(Migration42_43.class.getName());
+
+	private final DatabaseTypes dbTypes;
+
+	Migration42_43(DatabaseTypes dbTypes) {
+		this.dbTypes = dbTypes;
+	}
+
+	@Override
+	public int getStartVersion() {
+		return 42;
+	}
+
+	@Override
+	public int getEndVersion() {
+		return 43;
+	}
+
+	@Override
+	public void migrate(Connection txn) throws DbException {
+		Statement s = null;
+		try {
+			s = txn.createStatement();
+			s.execute(dbTypes.replaceTypes("ALTER TABLE localAuthors"
+					+ " ADD COLUMN handshakePublicKey _BINARY"));
+			s.execute(dbTypes.replaceTypes("ALTER TABLE localAuthors"
+					+ " ADD COLUMN handshakePrivateKey _BINARY"));
+			s.execute(dbTypes.replaceTypes("ALTER TABLE contacts"
+					+ " ADD COLUMN handshakePublicKey _BINARY"));
+			s.execute("ALTER TABLE contacts"
+					+ " DROP COLUMN active");
+		} catch (SQLException e) {
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/event/DefaultEventExecutorModule.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.event;
+
+import org.briarproject.bramble.api.event.EventExecutor;
+
+import java.util.concurrent.Executor;
+
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
+
+/**
+ * Default implementation of {@link EventExecutor} that uses a dedicated thread
+ * to notify listeners of events. Applications may prefer to supply an
+ * implementation that uses an existing thread, such as the UI thread.
+ */
+@Module
+public class DefaultEventExecutorModule {
+
+	@Provides
+	@Singleton
+	@EventExecutor
+	Executor provideEventExecutor() {
+		return newSingleThreadExecutor(r -> {
+			Thread t = new Thread(r);
+			t.setDaemon(true);
+			return t;
+		});
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/event/EventBusImpl.java

@@ -2,13 +2,16 @@ package org.briarproject.bramble.event;
 
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.util.Collection;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.Executor;
 
 import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
 
 @ThreadSafe
 @NotNullByDefault
@@ -16,6 +19,12 @@ class EventBusImpl implements EventBus {
 
 	private final Collection<EventListener> listeners =
 			new CopyOnWriteArrayList<>();
+	private final Executor eventExecutor;
+
+	@Inject
+	EventBusImpl(@EventExecutor Executor eventExecutor) {
+		this.eventExecutor = eventExecutor;
+	}
 
 	@Override
 	public void addListener(EventListener l) {
@@ -29,6 +38,8 @@ class EventBusImpl implements EventBus {
 
 	@Override
 	public void broadcast(Event e) {
-		for (EventListener l : listeners) l.eventOccurred(e);
+		eventExecutor.execute(() -> {
+			for (EventListener l : listeners) l.eventOccurred(e);
+		});
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/event/EventModule.java

@@ -12,7 +12,7 @@ public class EventModule {
 
 	@Provides
 	@Singleton
-	EventBus provideEventBus() {
-		return new EventBusImpl();
+	EventBus provideEventBus(EventBusImpl eventBus) {
+		return eventBus;
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/identity/AuthorFactoryImpl.java

@@ -1,12 +1,12 @@
 package org.briarproject.bramble.identity;
 
 import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.crypto.KeyPair;
 import org.briarproject.bramble.api.identity.Author;
 import org.briarproject.bramble.api.identity.AuthorFactory;
 import org.briarproject.bramble.api.identity.AuthorId;
 import org.briarproject.bramble.api.identity.LocalAuthor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.util.ByteUtils;
 import org.briarproject.bramble.util.StringUtils;
 
@@ -22,12 +22,10 @@ import static org.briarproject.bramble.util.ByteUtils.INT_32_BYTES;
 class AuthorFactoryImpl implements AuthorFactory {
 
 	private final CryptoComponent crypto;
-	private final Clock clock;
 
 	@Inject
-	AuthorFactoryImpl(CryptoComponent crypto, Clock clock) {
+	AuthorFactoryImpl(CryptoComponent crypto) {
 		this.crypto = crypto;
-		this.clock = clock;
 	}
 
 	@Override
@@ -43,17 +41,12 @@ class AuthorFactoryImpl implements AuthorFactory {
 	}
 
 	@Override
-	public LocalAuthor createLocalAuthor(String name, byte[] publicKey,
-			byte[] privateKey) {
-		return createLocalAuthor(FORMAT_VERSION, name, publicKey, privateKey);
-	}
-
-	@Override
-	public LocalAuthor createLocalAuthor(int formatVersion, String name,
-			byte[] publicKey, byte[] privateKey) {
-		AuthorId id = getId(formatVersion, name, publicKey);
-		return new LocalAuthor(id, formatVersion, name, publicKey, privateKey,
-				clock.currentTimeMillis());
+	public LocalAuthor createLocalAuthor(String name) {
+		KeyPair signatureKeyPair = crypto.generateSignatureKeyPair();
+		byte[] publicKey = signatureKeyPair.getPublic().getEncoded();
+		byte[] privateKey = signatureKeyPair.getPrivate().getEncoded();
+		AuthorId id = getId(FORMAT_VERSION, name, publicKey);
+		return new LocalAuthor(id, FORMAT_VERSION, name, publicKey, privateKey);
 	}
 
 	private AuthorId getId(int formatVersion, String name, byte[] publicKey) {

bramble-core/src/main/java/org/briarproject/bramble/identity/IdentityManagerImpl.java

@@ -6,97 +6,164 @@ import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.identity.AuthorFactory;
+import org.briarproject.bramble.api.identity.Identity;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager.OpenDatabaseHook;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.Clock;
 
+import java.util.Collection;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.now;
 
 @ThreadSafe
 @NotNullByDefault
-class IdentityManagerImpl implements IdentityManager {
+class IdentityManagerImpl implements IdentityManager, OpenDatabaseHook {
 
 	private static final Logger LOG =
-			Logger.getLogger(IdentityManagerImpl.class.getName());
+			getLogger(IdentityManagerImpl.class.getName());
 
 	private final DatabaseComponent db;
 	private final CryptoComponent crypto;
 	private final AuthorFactory authorFactory;
+	private final Clock clock;
 
-	// The local author is immutable so we can cache it
+	/**
+	 * The user's identity, or null if no identity has been registered or
+	 * loaded. If non-null, this identity always has handshake keys.
+	 */
 	@Nullable
-	private volatile LocalAuthor cachedAuthor;
+	private volatile Identity cachedIdentity = null;
+
+	/**
+	 * True if {@code cachedIdentity} was registered via
+	 * {@link #registerIdentity(Identity)} and should be stored when
+	 * {@link #onDatabaseOpened(Transaction)} is called.
+	 */
+
+	private volatile boolean shouldStoreIdentity = false;
+
+	/**
+	 * True if the handshake keys in {@code cachedIdentity} were generated
+	 * when the identity was loaded and should be stored when
+	 * {@link #onDatabaseOpened(Transaction)} is called.
+	 */
+	private volatile boolean shouldStoreKeys = false;
 
 	@Inject
 	IdentityManagerImpl(DatabaseComponent db, CryptoComponent crypto,
-			AuthorFactory authorFactory) {
+			AuthorFactory authorFactory, Clock clock) {
 		this.db = db;
 		this.crypto = crypto;
 		this.authorFactory = authorFactory;
+		this.clock = clock;
 	}
 
 	@Override
-	public LocalAuthor createLocalAuthor(String name) {
+	public Identity createIdentity(String name) {
 		long start = now();
-		KeyPair keyPair = crypto.generateSignatureKeyPair();
-		byte[] publicKey = keyPair.getPublic().getEncoded();
-		byte[] privateKey = keyPair.getPrivate().getEncoded();
-		LocalAuthor localAuthor = authorFactory.createLocalAuthor(name,
-				publicKey, privateKey);
-		logDuration(LOG, "Creating local author", start);
-		return localAuthor;
+		LocalAuthor localAuthor = authorFactory.createLocalAuthor(name);
+		KeyPair handshakeKeyPair = crypto.generateAgreementKeyPair();
+		byte[] handshakePub = handshakeKeyPair.getPublic().getEncoded();
+		byte[] handshakePriv = handshakeKeyPair.getPrivate().getEncoded();
+		logDuration(LOG, "Creating identity", start);
+		return new Identity(localAuthor, handshakePub, handshakePriv,
+				clock.currentTimeMillis());
 	}
 
 	@Override
-	public void registerLocalAuthor(LocalAuthor a) {
-		cachedAuthor = a;
-		LOG.info("Local author registered");
+	public void registerIdentity(Identity i) {
+		if (!i.hasHandshakeKeyPair()) throw new IllegalArgumentException();
+		cachedIdentity = i;
+		shouldStoreIdentity = true;
+		LOG.info("Identity registered");
 	}
 
 	@Override
-	public void storeLocalAuthor() throws DbException {
-		LocalAuthor cached = cachedAuthor;
-		if (cached == null) {
-			LOG.info("No local author to store");
-			return;
+	public void onDatabaseOpened(Transaction txn) throws DbException {
+		Identity cached = getCachedIdentity(txn);
+		if (shouldStoreIdentity) {
+			// The identity was registered at startup - store it
+			db.addIdentity(txn, cached);
+			LOG.info("Identity stored");
+		} else if (shouldStoreKeys) {
+			// Handshake keys were generated when loading the identity -
+			// store them
+			byte[] handshakePub =
+					requireNonNull(cached.getHandshakePublicKey());
+			byte[] handshakePriv =
+					requireNonNull(cached.getHandshakePrivateKey());
+			db.setHandshakeKeyPair(txn, cached.getId(), handshakePub,
+					handshakePriv);
+			LOG.info("Handshake key pair stored");
 		}
-		db.transaction(false, txn -> db.addLocalAuthor(txn, cached));
-		LOG.info("Local author stored");
 	}
 
 	@Override
 	public LocalAuthor getLocalAuthor() throws DbException {
-		if (cachedAuthor == null) {
-			cachedAuthor =
-					db.transactionWithResult(true, this::loadLocalAuthor);
-			LOG.info("Local author loaded");
-		}
-		LocalAuthor cached = cachedAuthor;
-		if (cached == null) throw new AssertionError();
-		return cached;
+		Identity cached = cachedIdentity;
+		if (cached == null)
+			cached = db.transactionWithResult(true, this::getCachedIdentity);
+		return cached.getLocalAuthor();
 	}
 
-
 	@Override
 	public LocalAuthor getLocalAuthor(Transaction txn) throws DbException {
-		if (cachedAuthor == null) {
-			cachedAuthor = loadLocalAuthor(txn);
-			LOG.info("Local author loaded");
-		}
-		LocalAuthor cached = cachedAuthor;
-		if (cached == null) throw new AssertionError();
+		return getCachedIdentity(txn).getLocalAuthor();
+	}
+
+	@Override
+	public byte[][] getHandshakeKeys(Transaction txn) throws DbException {
+		Identity cached = getCachedIdentity(txn);
+		return new byte[][] {
+				cached.getHandshakePublicKey(),
+				cached.getHandshakePrivateKey()
+		};
+	}
+
+	/**
+	 * Loads the identity if necessary and returns it. If
+	 * {@code cachedIdentity} was not already set by calling
+	 * {@link #registerIdentity(Identity)}, this method sets it. If
+	 * {@code cachedIdentity} was already set, either by calling
+	 * {@link #registerIdentity(Identity)} or by a previous call to this
+	 * method, then this method returns the cached identity without hitting
+	 * the database.
+	 */
+	private Identity getCachedIdentity(Transaction txn) throws DbException {
+		Identity cached = cachedIdentity;
+		if (cached == null)
+			cachedIdentity = cached = loadIdentityWithKeyPair(txn);
 		return cached;
 	}
 
-	private LocalAuthor loadLocalAuthor(Transaction txn) throws DbException {
-		return db.getLocalAuthors(txn).iterator().next();
+	/**
+	 * Loads and returns the identity, generating a handshake key pair if
+	 * necessary and setting {@code shouldStoreKeys} if a handshake key pair
+	 * was generated.
+	 */
+	private Identity loadIdentityWithKeyPair(Transaction txn)
+			throws DbException {
+		Collection<Identity> identities = db.getIdentities(txn);
+		if (identities.size() != 1) throw new DbException();
+		Identity i = identities.iterator().next();
+		LOG.info("Identity loaded");
+		if (i.hasHandshakeKeyPair()) return i;
+		KeyPair handshakeKeyPair = crypto.generateAgreementKeyPair();
+		byte[] handshakePub = handshakeKeyPair.getPublic().getEncoded();
+		byte[] handshakePriv = handshakeKeyPair.getPrivate().getEncoded();
+		LOG.info("Handshake key pair generated");
+		shouldStoreKeys = true;
+		return new Identity(i.getLocalAuthor(), handshakePub, handshakePriv,
+				i.getTimeCreated());
 	}
-
 }

bramble-core/src/main/java/org/briarproject/bramble/identity/IdentityModule.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.identity;
 
 import org.briarproject.bramble.api.identity.AuthorFactory;
 import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 
 import javax.inject.Inject;
 import javax.inject.Singleton;
@@ -24,8 +25,9 @@ public class IdentityModule {
 
 	@Provides
 	@Singleton
-	IdentityManager provideIdentityManager(
+	IdentityManager provideIdentityManager(LifecycleManager lifecycleManager,
 			IdentityManagerImpl identityManager) {
+		lifecycleManager.registerOpenDatabaseHook(identityManager);
 		return identityManager;
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/keyagreement/KeyAgreementProtocol.java

@@ -14,7 +14,7 @@ import java.io.IOException;
 import java.security.GeneralSecurityException;
 import java.util.Arrays;
 
-import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.MASTER_SECRET_LABEL;
+import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.MASTER_KEY_LABEL;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.PROTOCOL_VERSION;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.SHARED_SECRET_LABEL;
 
@@ -90,7 +90,7 @@ class KeyAgreementProtocol {
 	/**
 	 * Perform the BQP protocol.
 	 *
-	 * @return the negotiated master secret.
+	 * @return the negotiated master key.
 	 * @throws AbortException when the protocol may have been tampered with.
 	 * @throws IOException for all other other connection errors.
 	 */
@@ -115,7 +115,7 @@ class KeyAgreementProtocol {
 				receiveConfirm(s, theirPublicKey);
 				sendConfirm(s, theirPublicKey);
 			}
-			return crypto.deriveKey(MASTER_SECRET_LABEL, s);
+			return crypto.deriveKey(MASTER_KEY_LABEL, s);
 		} catch (AbortException e) {
 			sendAbort(e.getCause() != null);
 			throw e;

bramble-core/src/main/java/org/briarproject/bramble/keyagreement/KeyAgreementTaskImpl.java

@@ -114,9 +114,9 @@ class KeyAgreementTaskImpl extends Thread implements KeyAgreementTask,
 				keyAgreementCrypto, payloadEncoder, transport, remotePayload,
 				localPayload, localKeyPair, alice);
 		try {
-			SecretKey master = protocol.perform();
+			SecretKey masterKey = protocol.perform();
 			KeyAgreementResult result =
-					new KeyAgreementResult(master, transport.getConnection(),
+					new KeyAgreementResult(masterKey, transport.getConnection(),
 							transport.getTransportId(), alice);
 			LOG.info("Finished BQP protocol");
 			// Broadcast result to caller

bramble-core/src/main/java/org/briarproject/bramble/keyagreement/PayloadParserImpl.java

@@ -1,13 +1,13 @@
 package org.briarproject.bramble.keyagreement;
 
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.UnsupportedVersionException;
 import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.data.BdfReader;
 import org.briarproject.bramble.api.data.BdfReaderFactory;
 import org.briarproject.bramble.api.keyagreement.Payload;
 import org.briarproject.bramble.api.keyagreement.PayloadParser;
 import org.briarproject.bramble.api.keyagreement.TransportDescriptor;
-import org.briarproject.bramble.api.keyagreement.UnsupportedVersionException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.BluetoothConstants;
 import org.briarproject.bramble.api.plugin.LanTcpConstants;

bramble-core/src/main/java/org/briarproject/bramble/lifecycle/LifecycleManagerImpl.java

@@ -7,13 +7,11 @@ import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.lifecycle.ServiceException;
 import org.briarproject.bramble.api.lifecycle.event.LifecycleEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.sync.Client;
 
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
@@ -28,6 +26,7 @@ import javax.inject.Inject;
 import static java.util.logging.Level.FINE;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.COMPACTING_DATABASE;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.MIGRATING_DATABASE;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.RUNNING;
@@ -49,14 +48,13 @@ import static org.briarproject.bramble.util.LogUtils.now;
 class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 
 	private static final Logger LOG =
-			Logger.getLogger(LifecycleManagerImpl.class.getName());
+			getLogger(LifecycleManagerImpl.class.getName());
 
 	private final DatabaseComponent db;
 	private final EventBus eventBus;
 	private final List<Service> services;
-	private final List<Client> clients;
+	private final List<OpenDatabaseHook> openDatabaseHooks;
 	private final List<ExecutorService> executors;
-	private final IdentityManager identityManager;
 	private final Semaphore startStopSemaphore = new Semaphore(1);
 	private final CountDownLatch dbLatch = new CountDownLatch(1);
 	private final CountDownLatch startupLatch = new CountDownLatch(1);
@@ -65,13 +63,11 @@ class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 	private volatile LifecycleState state = STARTING;
 
 	@Inject
-	LifecycleManagerImpl(DatabaseComponent db, EventBus eventBus,
-			IdentityManager identityManager) {
+	LifecycleManagerImpl(DatabaseComponent db, EventBus eventBus) {
 		this.db = db;
 		this.eventBus = eventBus;
-		this.identityManager = identityManager;
 		services = new CopyOnWriteArrayList<>();
-		clients = new CopyOnWriteArrayList<>();
+		openDatabaseHooks = new CopyOnWriteArrayList<>();
 		executors = new CopyOnWriteArrayList<>();
 	}
 
@@ -83,10 +79,12 @@ class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 	}
 
 	@Override
-	public void registerClient(Client c) {
-		if (LOG.isLoggable(INFO))
-			LOG.info("Registering client " + c.getClass().getSimpleName());
-		clients.add(c);
+	public void registerOpenDatabaseHook(OpenDatabaseHook hook) {
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("Registering open database hook "
+					+ hook.getClass().getSimpleName());
+		}
+		openDatabaseHooks.add(hook);
 	}
 
 	@Override
@@ -102,28 +100,28 @@ class LifecycleManagerImpl implements LifecycleManager, MigrationListener {
 			return ALREADY_RUNNING;
 		}
 		try {
-			LOG.info("Starting services");
+			LOG.info("Opening database");
 			long start = now();
-
 			boolean reopened = db.open(dbKey, this);
 			if (reopened) logDuration(LOG, "Reopening database", start);
 			else logDuration(LOG, "Creating database", start);
-			identityManager.storeLocalAuthor();
 
+			db.transaction(false, txn -> {
+				for (OpenDatabaseHook hook : openDatabaseHooks) {
+					long start1 = now();
+					hook.onDatabaseOpened(txn);
+					if (LOG.isLoggable(FINE)) {
+						logDuration(LOG, "Calling open database hook "
+								+ hook.getClass().getSimpleName(), start1);
+					}
+				}
+			});
+
+			LOG.info("Starting services");
 			state = STARTING_SERVICES;
 			dbLatch.countDown();
 			eventBus.broadcast(new LifecycleEvent(STARTING_SERVICES));
 
-			db.transaction(false, txn -> {
-				for (Client c : clients) {
-					long start1 = now();
-					c.createLocalState(txn);
-					if (LOG.isLoggable(FINE)) {
-						logDuration(LOG, "Starting client "
-								+ c.getClass().getSimpleName(), start1);
-					}
-				}
-			});
 			for (Service s : services) {
 				start = now();
 				s.startService();

bramble-core/src/main/java/org/briarproject/bramble/plugin/PluginManagerImpl.java

@@ -8,7 +8,6 @@ import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.lifecycle.ServiceException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.PluginConfig;
@@ -30,10 +29,7 @@ import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
 import org.briarproject.bramble.api.settings.Settings;
 import org.briarproject.bramble.api.settings.SettingsManager;
-import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
 
-import java.security.SecureRandom;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -42,7 +38,6 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
@@ -64,15 +59,11 @@ class PluginManagerImpl implements PluginManager, Service {
 			Logger.getLogger(PluginManagerImpl.class.getName());
 
 	private final Executor ioExecutor;
-	private final ScheduledExecutorService scheduler;
 	private final EventBus eventBus;
 	private final PluginConfig pluginConfig;
 	private final ConnectionManager connectionManager;
-	private final ConnectionRegistry connectionRegistry;
 	private final SettingsManager settingsManager;
 	private final TransportPropertyManager transportPropertyManager;
-	private final SecureRandom random;
-	private final Clock clock;
 	private final Map<TransportId, Plugin> plugins;
 	private final List<SimplexPlugin> simplexPlugins;
 	private final List<DuplexPlugin> duplexPlugins;
@@ -80,41 +71,25 @@ class PluginManagerImpl implements PluginManager, Service {
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
 	@Inject
-	PluginManagerImpl(@IoExecutor Executor ioExecutor,
-			@Scheduler ScheduledExecutorService scheduler, EventBus eventBus,
+	PluginManagerImpl(@IoExecutor Executor ioExecutor, EventBus eventBus,
 			PluginConfig pluginConfig, ConnectionManager connectionManager,
-			ConnectionRegistry connectionRegistry,
 			SettingsManager settingsManager,
-			TransportPropertyManager transportPropertyManager,
-			SecureRandom random, Clock clock) {
+			TransportPropertyManager transportPropertyManager) {
 		this.ioExecutor = ioExecutor;
-		this.scheduler = scheduler;
 		this.eventBus = eventBus;
 		this.pluginConfig = pluginConfig;
 		this.connectionManager = connectionManager;
-		this.connectionRegistry = connectionRegistry;
 		this.settingsManager = settingsManager;
 		this.transportPropertyManager = transportPropertyManager;
-		this.random = random;
-		this.clock = clock;
 		plugins = new ConcurrentHashMap<>();
 		simplexPlugins = new CopyOnWriteArrayList<>();
 		duplexPlugins = new CopyOnWriteArrayList<>();
 		startLatches = new ConcurrentHashMap<>();
-
 	}
 
 	@Override
 	public void startService() {
 		if (used.getAndSet(true)) throw new IllegalStateException();
-		// Instantiate the poller
-		if (pluginConfig.shouldPoll()) {
-			LOG.info("Starting poller");
-			Poller poller = new Poller(ioExecutor, scheduler, connectionManager,
-					connectionRegistry, this, transportPropertyManager, random,
-					clock);
-			eventBus.addListener(poller);
-		}
 		// Instantiate the simplex plugins and start them asynchronously
 		LOG.info("Starting simplex plugins");
 		for (SimplexPluginFactory f : pluginConfig.getSimplexFactories()) {

bramble-core/src/main/java/org/briarproject/bramble/plugin/PluginModule.java

@@ -1,9 +1,11 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
 import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.ConnectionRegistry;
+import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.PluginManager;
 
 import javax.inject.Inject;
@@ -18,6 +20,8 @@ public class PluginModule {
 	public static class EagerSingletons {
 		@Inject
 		PluginManager pluginManager;
+		@Inject
+		Poller poller;
 	}
 
 	@Provides
@@ -46,4 +50,12 @@ public class PluginModule {
 		lifecycleManager.registerService(pluginManager);
 		return pluginManager;
 	}
+
+	@Provides
+	@Singleton
+	Poller providePoller(PluginConfig config, EventBus eventBus,
+			PollerImpl poller) {
+		if (config.shouldPoll()) eventBus.addListener(poller);
+		return poller;
+	}
 }